CHAPTER 2

Hemostasis and Thrombosis

2.1 Coagulation and Fibrinolytic Systems/Reagents and Methods

2.2 Platelet and Vascular Disorders
2.3 Coagulation System Disorders
2.4 Inhibitors, Thrombotic Disorders, and Anticoagulant Drugs
2.5 Hemostasis Problem-Solving
 2.1
Coagulation and Fibrinolytic Systems/Reagents and
Methods
1. Which of the following initiates in vivo coagulation by activation of factor VII?
A. Protein C
B. Tissue factor (TF)
C. Plasmin activator
D. Thrombomodulin (TM)
Hemostasis/Apply knowledge of fundamental biological characteristics/Coagulation/2

Answer to Question 1
1. B In vivo, activation of coagulation occurs on the surface of activated platelets (PLTs) or
cells that have TF. TF is found on the surface of many cells outside the vascular
system (extrinsic). On vascular injury, TF is exposed to the vascular system. TF has
high affinity for factors VII and VIIa. TF activates factor VII to VIIa and forms TF–
VIIa complex. TF–VIIa complex in the presence of calcium ion (Ca2+) and PLT
phospholipid activates factor IX to factor IXa and factor X to factor Xa. Factor Xa
forms a complex with cofactor Va (Xa–Va) on the surface of the activated PLTs.
Factor Xa–Va complex in the presence of Ca2+ and PLT phospholipid converts
prothrombin (factor II) to thrombin (IIa). Thrombin acts on soluble plasma fibrinogen
to form a fibrin clot, which is stabilized by activated factor XIII (XIIIa). In addition,
activated factor IX (IXa) forms a complex with activated cofactor VIII (VIIIa) on the
surface of the activated PLTs. Factor IXa–VIIIa complex in the presence of Ca2+ and
PLT phospholipid converts factor X to Xa with the end products of thrombin and fibrin
clot, as discussed previously. The classical description of intrinsic, extrinsic, and
common pathways does not take place in vivo. The concept of these three pathways is
used to explain clot formation in laboratory tests. Activated thromboplastin time
(APTT) is determined by the intrinsic and common pathways, whereas prothrombin
time (PT) is determined by the extrinsic and common pathways. The extrinsic pathway
is so named because TF is derived from extravascular cells.

2. Which of the following clotting factors plays a role in clot formation in vitro, but not in
vivo?
A. Factor VIIa
B. Factor IIa
C. Factor XIIa
D. Factor Xa
Hemostasis/Apply knowledge of fundamental biological characteristics/Coagulation/2
3. The anticoagulant of choice for most routine coagulation studies is:
 A. Sodium oxalate
B. Sodium citrate
C. Heparin
D. Ethylenediaminetetraacetic acid (EDTA)
Hemostasis/Select methods/Reagents/Specimen collection and handling/Specimen/1
4. Which anticoagulant:blood ratio is correct for coagulation procedures?
A. 1:4
B. 1:5
C. 1:9
D. 1:10
Hemostasis/Select methods/Reagents/Specimen collection and handling/Specimen/1
5. Which results would be expected for PT and APTT in a patient with polycythemia?
A. Both prolonged
B. Both shortened
C. Normal PT, prolonged APTT
D. Both normal
Hemostasis/Correlate clinical and laboratory data/Coagulation tests/3
6. Which reagents are used in the PT test?
A. Thromboplastin and sodium chloride
B. Thromboplastin and potassium chloride
C. Thromboplastin and calcium
D. Actin and calcium chloride
Hemostasis/Select methods/Reagents/Coagulation tests/1
7. Which test would be abnormal in a patient with factor X deficiency?
A. PT only
B. APTT only
C. PT and APTT
D. Thrombin time (TT)
Hemostasis/Correlate clinical and laboratory data/Coagulation tests/2

Answers to Questions 2–7

2. C Factor XIIa does not play a role in coagulation in vivo; however, in vitro, the
deficiency of this factor causes prolonged APTT. In vitro, factor XII is activated by
substances, such as glass, Kaolin, and ellagic acid, and in vivo it may be activated by
exposure to a negatively charged cell surface membrane, such collagen, as well as to
kallikrein and high-molecular-weight kininogen (HMWK). In vivo, factor XIIa plays
an important role in the fibrinolytic system by activating plasminogen to plasmin.
Plasmin degrades the fibrin clot at the site of injury. Deficiency of factor XII is
associated with thrombosis and not with bleeding. Factors VIIa, Xa, and IIa play a role
in vivo and in vitro.
3. B The anticoagulant of choice for most coagulation procedures is sodium citrate (3.2%).
Because factors V and VIII are more labile in sodium oxalate, heparin neutralizes
thrombin, and EDTA inhibits thrombin’s action on fibrinogen, these anticoagulants are
not used for routine coagulation studies.
 4. C The optimal anticoagulant:blood ratio is one part anticoagulant to nine parts blood. The
anticoagulant supplied in this amount is sufficient to bind all the available calcium,
thereby preventing clotting.
5. A The volume of blood in a polycythemic patient contains so little plasma that excess
anticoagulant remains and is available to bind to reagent calcium, thereby resulting in
prolongation of PT and APTT. For more accurate results, the plasma:anticoagulant
ratio can be modified by decreasing the amount of anticoagulant in the collection tube
by using the following formula: (0.00185)(V)(100–H) = C, where V = blood volume in
milliliters (mL); H = patient’s hematocrit (Hct); and C = volume (mL) of
anticoagulant. A new sample should be drawn to rerun the PT and APTT tests.
6. C Thromboplastin and calcium (combined into a single reagent) replace tissue
thromboplastin and calcium necessary, in vivo, to activate factor VII to factor VIIa.
This ultimately generates thrombin from prothrombin via the coagulation cascade.
7. C Factor X is involved in the common pathway of the coagulation cascade; therefore, its
deficiency prolongs both PT and APTT. Activated factor X along with activated factor
V in the presence of calcium and platelet factor 3 (PF3) converts prothrombin (factor
II) to the active enzyme thrombin (factor IIa).

8. Which clotting factor is not measured by the PT and APTT tests?

A. Factor VIII
B. Factor IX
C. Factor V
D. Factor XIII
Hemostasis/Apply principles of basic laboratory procedures/Coagulation tests/1
9. A modification of which procedure can be used to measure fibrinogen?
A. PT
B. APTT
C. TT
D. Fibrin degradation products
Hemostasis/Apply principles of basic laboratory procedures/Coagulation tests/2
10. Which of the following characterizes vitamin K?
A. It is required for biological activity of fibrinolysis
B. Its activity is enhanced by heparin therapy
C. It is required for carboxylation of glutamate residues of some coagulation factors
D. It is made by endothelial cells
Hemostasis/Apply knowledge of fundamental biological characteristics/Vitamin K/2
11. Which fragments of fibrin clot degradation are measured by the D-dimer test?
A. Fragments X and Y
B. Fibrinopeptide A and B
C. Fragments D and E
D. The D-D domains
Hemostasis/Apply principles of basic laboratory procedures/D-dimer/2
12. Which of the following clotting factors are measured by the APTT test?
A. Factors II, VII, IX, X
 B. Factors VII, X, V, II, I
C. Factors XII, XI, IX, VIII, X, V, II, I
D. Factors XII, VII, X, V, II, I
Hemostasis/Correlate clinical and laboratory data/Coagulation tests/2
13. Which coagulation test(s) would be abnormal in a patient with vitamin K deficiency?
A. PT only
B. PT and APTT
C. Fibrinogen level
D. TT
Hemostasis/Correlate clinical and laboratory data/Coagulation tests/2

Answers to Questions 8–14

8. D Factor XIII is not measured by PT or APTT. Factor XIII (fibrin stabilizing factor) is a
transamidase. It creates covalent bonds between fibrin monomers, which are formed
during the coagulation process, to produce a stable fibrin clot. In the absence of factor
XIII, the hydrogen bonded fibrin polymers are unstable and, therefore, soluble in 5M
urea or in 1% monochloroacetic acid.
9. C Fibrinogen can be quantitatively measured by modification of the TT by diluting the
plasma because the thrombin clotting time of diluted plasma is inversely proportional
to the concentration of fibrinogen (principle of Clauss method).
10. C Vitamin K is necessary for activation of vitamin K–dependent clotting factors (II,
VII, IX, and X). This activation is accomplished by carboxylation of glutamic acid
residues of the inactive clotting factors. The activity of vitamin K is not enhanced by
heparin therapy. Vitamin K is present in a variety of foods and is also the only vitamin
made by the organisms living in the intestine.
11. D D-dimer is a specific product resulting from digestion of cross-linked fibrin only. It
consists of two D domains called D-D fragment and is a marker for thrombosis and
fibrinolysis. In the D-dimer test, monoclonal antibody is directed against D-dimer
antigen by using a variety of automated instruments. The D-dimer test is used to
diagnose acute and chronic disseminated intravascular coagulation (DIC) and to rule
out thromboembolic disorders. Fragments X, Y, D, and E are produced by the action of
plasmin on fibrinogen and fibrin. Polypeptide A and B are produced by the proteolytic
action of thrombin on fibrinogen to form a fibrin clot.
12. C The APTT test evaluates the clotting factors in the intrinsic pathway (XII, XI, IX, and
VIII) as well as those in the common pathway (X, V, II, and I).
13. B Patients with vitamin K deficiency exhibit decreased production of functional
prothrombin proteins (factors II, VII, IX, and X). Decreased levels of these factors
prolong both PT and APTT.

14. Which of the following is correct regarding the international normalized ratio (INR)?
A. It uses the international sensitivity ratio (ISR)
B. It standardizes PT results
C. It standardizes APTT results
 D. It is used to monitor heparin therapy
Hemostasis/Apply knowledge of fundamental biological characteristics/INR/2
15. Which of the following is referred to as an endogenous activator of plasminogen?
A. Streptokinase
B. Transamidase
C. Tissue plasminogen activator (tPA)
D. tPA inhibitor
Hemostasis/Apply knowledge of fundamental biological characteristics/Plasminogen/2
16. Which protein is the primary inhibitor of the fibrinolytic system?
A. Protein C
B. Protein S
C. α2-Antiplasmin
D. α2-Macroglobulin
Hemostasis/Apply knowledge of fundamental biological characteristics/Plasmin/1
17. Which of the following statements is correct regarding the D-dimer test?
A. Levels are decreased in DIC
B. Test detects polypeptides A and B
C. Test detects fragments D and E
D. Test has a negative predictive value
Hemostasis/Apply principles of basic laboratory procedures/D-dimer/2
18. A protein that plays a role in both coagulation and PLT aggregation is:
A. Factor I
B. Factor VIII
C. Factor IX
D. Factor XI
Hemostasis/Apply knowledge of fundamental biological characteristics/Clotting factors/2
19. A standard 4.5-mL blue-top tube filled with 3.0 mL of blood was submitted to the
laboratory for PT and APTT tests. The sample is from a patient undergoing surgery the
following morning for a tonsillectomy. Which of the following is the necessary course of
action by the medical laboratory scientist?
A. Run both tests in duplicate and report the average result
B. Reject the sample and request a new sample
C. Report the PT result
D. Report the APTT result
Hemostasis/Select methods/Reagents/Specimen collection and handling/Specimens/3

Answers to Questions 14–19

14. B INR is used to standardize PT results to adjust for the differences in thromboplastin
reagents made by different manufacturers and used by various institutions. The INR
calculation uses the international sensitivity index (ISI) value and is used to monitor an
oral anticoagulant, such as warfarin. INR is not used to standardize APTT testing.
15. C tPA is an endogenous (produced in the body) activator of plasminogen. It is released
from the endothelial cells by the action of protein C. It converts plasminogen to
 plasmin. Streptokinase is an exogenous (not made in the body) activator of
plasminogen.
16. C α2-Antiplasmin is the main inhibitor of plasmin. It inhibits plasmin by forming a 1:1
stoichiometric complex with any free plasmin in plasma and, thus, prevents binding of
plasmin to fibrin and fibrinogen.
17. D The D-dimer assay evaluates fibrin degradation. It is a nonspecific screening test that
shows increased values in many conditions in which fibrinolysis is increased, such as
DIC and fibrinolytic therapy. The D-dimer test is widely used to rule out thrombosis
and thrombotic activities. The negative predictive value of a test is the probability that
a person with a negative result is free of the disease that the test is meant to detect.
Therefore, a negative D-dimer test result rules out thrombosis, and further laboratory
investigations are not required.
18. A Factor I (fibrinogen), along with the glycoprotein IIb–IIIa complex, is necessary for
PLT aggregation. Factor I is also a substrate in the common pathway of coagulation.
Thrombin acts on fibrinogen to form fibrin clots.
19. B A 4.5-mL blue-top tube contains 4.5 mL blood + 0.5 mL sodium citrate. The tube
should be 90% full. A tube with 3.0 mL blood should be rejected because the quantity
is not sufficient (QNS). QNS samples alter the necessary blood:anticoagulant ratio
(9:1). The excess anticoagulant in a QNS sample binds to the reagent calcium,
resulting in prolongation of PT and APTT.

20. Which statement is correct regarding sample storage for the PT test?
A. Stable for 24 hours if the sample is capped
B. Stable for 24 hours if the sample is refrigerated at 4°C
C. Stable for 4 hours if the sample is stored at 4°C
D. Should be run within 8 hours
Hemostasis/Select methods/Reagents/Specimen collection and handling/Specimens/2
21. In primary fibrinolysis, the fibrinolytic activity results in response to:
A. Increased fibrin formation
B. Spontaneous activation of fibrinolysis
C. Increased fibrin monomers
D. DIC
Hemostasis/Apply knowledge of fundamental biological characteristics/Fibrinolysis/2
22. Plasminogen deficiency is associated with:
A. Bleeding
B. Thrombosis
C. Increased fibrinolysis
D. Increased coagulation
Hemostasis/Correlate clinical and laboratory data/Plasminogen/2
23. Which of the following clotting factors are activated by thrombin that is generated by
tissue pathway (TF-VIIa)?
A. Factors XII, XI
B. Factors XII, I
C. Factors I, II
 D. Factors V, VIII
Hemostasis/Apply knowledge of fundamental biological characteristics/Thrombin/2
24. Which substrate is used in a chromogenic factor assay?
A. p-nitroaniline (pNa)
B. Chlorophenol red
C. Prussian blue
D. Ferricyanide
Hemostasis/Selected methods/Reagents/Chromogenic assays/1
25. Which of the following antibodies is used in the D-dimer assay?
A. Polyclonal antibody directed against X and Y fragments
B. Polyclonal antibody directed against D-dimer
C. Monoclonal antibody against D and E fragments
D. Monoclonal antibody against D-dimer
Hemostasis/Selected methods/Reagents/D-dimer assay/2

Answers to Questions 20–25

20. A According to Clinical Laboratory Standards Institute (CLSI) guidelines, plasma
samples for PT testing, if capped, are stable for 24 hours at room temperature.
Refrigerating the sample causes cold activation of factor VII and, therefore, shortened
PT results. APTT samples are stable for 4 hours if stored at 4°C.
21. B Primary fibrinolysis is a rare pathological condition in which spontaneous systemic
fibrinolysis occurs. Plasmin is formed in the absence of coagulation activation and clot
formation. Primary fibrinolysis is associated with increased production of plasminogen
and plasmin, decreased plasmin removal from the circulation, and spontaneous
bleeding.
22. B Plasminogen deficiency is associated with thrombosis. Plasminogen is an important
component of the fibrinolytic system. Plasminogen is activated to plasmin, which is
necessary for the degradation of fibrin clots to prevent thrombosis. When plasminogen
is deficient, plasmin is not formed, causing a defect in the clot lysing processes.
23. D Factors V and VIII are activated by the thrombin that is generated by the action of
TF-VIIa on factor X to form factor Xa. Factor Xa forms a complex with factor Va on
the PLT surfaces. Factor Xa–Va complex in the presence of phospholipid and Ca2+
transform more prothrombin to thrombin.
24. A The chromogenic, or amidolytic, assays use a color-producing substance, known as
chromophore. The chromophore used for the coagulation laboratory is pNa. pNa is
bound to a synthetic oligopeptide substrate. The protease cleaves the chromogenic
substrate at the site binding the oligopeptide to the pNa, which results in release of
pNa. Free pNa has a yellow color; the color intensity of the solution is proportional to
protease activity and is measured by a photodetector at 405 nm.
25. D The D-dimer is the fibrin degradation product generated by the action of plasmin on
cross-linked fibrin formed by XIIIa. The patient’s plasma is mixed with latex particles
coated with monoclonal antibodies against D-domains. The test can be automated, or
performed manually on a glass slide by looking macroscopically for agglutination.
Enzyme-linked immunosorbent assay (ELISA) methods are also available. Normal D-
dimer in plasma is less than 2 ng/mL. Increased levels of D-dimer are associated with
DIC, thrombolytic therapy, venous thrombosis, and thromboembolic disorders. The D-
dimer assay has a 90% to 95% negative predictive value and has been used to rule out
thrombosis and thromboembolic disorders.
 2.2
Platelet and Vascular Disorders
1. Thrombotic thrombocytopenic purpura (TTP) is characterized by:
A. Prolonged PT
B. Increased PLT aggregation
C. Thrombocytosis
D. Prolonged APTT
Hemostasis/Correlate clinical and laboratory data/Platelets/2
2. Thrombocytopenia may be associated with:
A. Splenectomy
B. Hypersplenism
C. Acute blood loss
D. Increased proliferation of pluripotent stem cells
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelets/2
3. Aspirin prevents PLT aggregation by inhibiting the action of which enzyme?
A. Phospholipase
B. Cyclo-oxygenase
C. Thromboxane A2 (TXA2) synthetase
D. Prostacyclin synthetase
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelets/1
4. Normal PLT adhesion depends on:
A. Fibrinogen
B. Glycoprotein Ib
C. Glycoprotein IIb–IIIa complex
D. Calcium
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelets/1
5. Which of the following test results is normal in a patient with classic von Willebrand
disease?
A. PLT aggregation
B. APTT
C. PLT count
D. Factor VIII:C and von Willebrand factor (VWF) levels
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/2
6. Bernard–Soulier syndrome is associated with:
A. Decreased factor IX
B. Decreased factor VIII
C. Thrombocytopenia and giant PLTs
D. Abnormal PLT function test results
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/2
 Answers to Questions 1–6
1. B TTP is a quantitative PLT disorder associated with increased intravascular PLT
activation and aggregation resulting in thrombocytopenia. PT and APTT results are
normal in TTP.
2. B Hypersplenism is associated with thrombocytopenia. In this condition, up to 90% of
PLTs can be sequestered in the spleen, causing decreases in circulatory PLTs.
Splenectomy, acute blood loss, and increased proliferation of pluripotent stem cells are
associated with thrombocytosis.
3. B Aspirin prevents PLT aggregation by inhibiting the activity of the enzyme cyclo-
oxygenase. This inhibition prevents the formation of TXA2, which serves as a potent
PLT aggregator.
4. B Glycoprotein Ib is a PLT receptor for VWF. Glycoprotein Ib and VWF are both
necessary for a normal PLT adhesion. Other proteins that play a role in PLT adhesion
are glycoproteins V and IX.
5. C Von Willebrand disease is an inherited, qualitative PLT disorder that results in
increased bleeding, prolonged APTT, and decreased factor VIII:C and VWF levels.
The PLT count and morphology are generally normal in von Willebrand disease, but
PLT aggregation in the PLT function assay is abnormal.
6. C Bernard–Soulier syndrome is associated with thrombocytopenia and giant PLTs. It is a
qualitative PLT disorder caused by the deficiency of glycoprotein Ib. In Bernard–
Soulier syndrome, PLT aggregation in the PLT function assay is abnormal. Factor VIII
and IX assays are not indicated for this diagnosis.

7. When performing PLT aggregation studies, which set of PLT aggregation results would
most likely be associated with Bernard–Soulier syndrome?
A. Normal PLT aggregation to collagen, adenosine diphosphate (ADP), and ristocetin
B. Normal PLT aggregation to collagen, ADP, and epinephrine (EPI); decreased aggregation
to ristocetin
C. Normal PLT aggregation to EPI and ristocetin; decreased aggregation to collagen and
ADP
D. Normal PLT aggregation to EPI, ristocetin, and collagen; decreased aggregation to ADP
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/2
8. Which set of PLT responses would be most likely associated with Glanzmann
thrombasthenia?
A. Normal PLT aggregation to ADP and ristocetin; decreased aggregation to collagen
B. Normal PLT aggregation to collagen; decreased aggregation to ADP and ristocetin
C. Normal PLT aggregation to ristocetin; decreased aggregation to collagen, ADP, and EPI
D. Normal PLT aggregation to ADP; decreased aggregation to collagen and ristocetin
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/2
9. Which of the following is a characteristic of acute immune thrombocytopenic purpura?
A. Spontaneous remission within a few weeks
B. Predominantly seen in adults
C. Nonimmune PLT destruction
 D. Insidious onset
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelet disorders/2
10. TTP differs from DIC in that:
A. APTT is normal in TTP but prolonged in DIC
B. Schistocytes are not present in TTP but are present in DIC
C. PLT count is decreased in TTP but normal in DIC
D. PT is prolonged in TTP but decreased in DIC
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/2
11. Several hours after birth, a baby boy develops petechiae and purpura and hemorrhagic
diathesis. The PLT count is 18 × 109/L. What is the most likely explanation for the low
PLT count?
A. Drug-induced thrombocytopenia
B. Secondary thrombocytopenia
C. Neonatal alloimmune thrombocytopenia
D. Neonatal DIC
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/3

Answers to Questions 7–11

7. B Bernard–Soulier syndrome is a disorder of PLT adhesion caused by deficiency of
glycoprotein Ib. PLT aggregation is normal in response to collagen, ADP, and EPI but
abnormal in response to ristocetin.
8. C Glanzmann thrombasthenia is a disorder of PLT aggregation. PLT aggregation is
normal in response to ristocetin, but abnormal in response to collagen, ADP, and EPI.
9. A Acute immune thrombocytopenic purpura is an immune-mediated disorder found
predominantly in children. It is commonly associated with infection (primarily viral). It
is characterized by abrupt onset, and spontaneous remission usually occurs within
several weeks.
10. A TTP is a PLT disorder in which PLT aggregation increases, resulting in
thrombocytopenia. Schistocytes are present in TTP as a result of microangiopathic
hemolytic anemia (MAHA); however, the PT and APTT are both normal. In DIC, the
PT and APTT are both prolonged, the PLT count is decreased, and schistocytes are
seen in the peripheral blood smear.
11. C Neonatal alloimmune thrombocytopenia is similar to the hemolytic disease of the
fetus and newborn. It results from immunization of the mother by fetal PLT antigens.
The offending antibodies are commonly anti-PLT antigen A1 (PlA1), also referred to as
human platelet antigen (HPA) 1a. These alloantibodies are directed against
glycoproteins IIb/IIIa, Ib/IX, Ia/IIb, and CD 109. Maternal antibodies cross the
placenta, resulting in thrombocytopenia in the fetus.

12. Which of the following is associated with post-transfusion purpura (PTP)?

A. Nonimmune thrombocytopenia/alloantibodies
B. Immune-mediated thrombocytopenia/alloantibodies
C. Immune-mediated thrombocytopenia/autoantibodies
 D. Nonimmune-mediated thrombocytopenia/autoantibodies
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelet disorders/2
13. Hemolytic uremic syndrome (HUS) is associated with:
A. Fever, thrombocytosis, anemia, and renal failure
B. Fever, granulocytosis, and thrombocytosis
C. Escherichia coli 0157:H7
D. Leukocytosis and thrombocytosis
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelet disorders/2
14. Storage pool deficiencies are defects of:
A. PLT adhesion
B. PLT aggregation
C. PLT granules
D. PLT production
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelet disorders/1
15. Lumi-aggregation measures:
A. PLT aggregation only
B. PLT aggregation and adenosine triphosphate (ATP) release
C. PLT adhesion
D. PLT glycoprotein Ib
Hemostasis/Select methods/Reagents/Specimen collection and handling/Aggregometry/1
16. Neurological findings may be commonly associated with which of the following
disorders?
A. HUS
B. TTP
C. ITP
D. PTP
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelet function/1
17. Which of the following is correct regarding acquired TTP?
A. Autoimmune disease
B. Decreased VWF
C. Decreased PLT aggregation
D. Decreased PLT adhesion
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelet disorders/2
18. Hereditary hemorrhagic telangiectasia is a disorder of:
A. PLTs
B. Clotting proteins
C. Fibrinolysis
D. Connective tissue
Hemostasis/Apply knowledge of fundamental biological characteristics/2

Answers to Questions 12–18

12. B PTP is a rare form of alloimmune thrombocytopenia characterized by severe
thrombocytopenia occurring after transfusion of blood or blood products. PTP is
caused by antibody-related PLT destruction in previously immunized patients. In the
 majority of cases, the alloantibody produced is against PlA1 (HPA-1a).
13. C HUS is caused by E. coli 0157:H7. It is associated with ingestion of E. coli–
contaminated foods and is commonly seen in children. The clinical manifestations in
HUS are fever, diarrhea, thrombocytopenia, MAHA, and renal failure.
14. C Storage pool deficiencies are defects of PLT granules. Most commonly, a decrease in
PLT-dense granules is present with decreased release of ADP, ATP, calcium, and
serotonin from PLT-dense granules.
15. B Lumi-aggregation measures PLT aggregation and ATP release. It is performed on
whole blood diluted with saline. PLT aggregation is measured by impedance, whereas
ATP release is measured by addition of luciferin to a blood sample. There is no ATP
release in storage pool deficiencies.
16. B TTP is characterized by neurological problems, fever, thrombocytopenia, MAHA, and
renal failure.
17. A Acquired TTP is an autoimmune disease associated with autoantibodies produced
against VWF cleaving enzyme (ADAMTS-13). This deficiency results in an increase
in plasma VWF and consequently increased PLT aggregation and thrombocytopenia.
18. D Hereditary hemorrhagic telangiectasia (Osler–Weber–Rendu syndrome) is a
connective tissue disorder associated with telangiectases (dilated capillaries) of the
mucous membranes and skin. Lesions may develop on the tongue, lips, palate, face,
hands, and nasal mucosa and throughout the gastrointestinal tract. This disorder is an
autosomal dominant condition that usually manifests in adolescence or early
adulthood.

19. Which of the following prevents PLT aggregation?

A. TXA2
B. Thromboxane B2
C. Prostacyclin
D. Antithrombin (AT)
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelets/2
20. Which defect characterizes Gray syndrome?
A. PLT adhesion defect
B. Dense granule defect
C. Alpha granule defect
D. Coagulation defect
Hemostasis/Apply knowledge of fundamental biological characteristics/Platelet disorders/2
21. The P2Y12 ADP receptor agonist assay may be used to monitor PLT aggregation
inhibition to which of the following drugs?
A. Warfarin
B. Heparin
C. Low-molecular-weight heparin (LMWH)
D. Clopidogrel (Plavix)
Hemostasis/Selected methods/Reagents/Special tests/2
 Answers to Questions 19–21
19. C Prostacyclin is released from the endothelium and is an inhibitor of PLT aggregation.
TXA2 promotes PLT aggregation. Thromboxane B2 is an oxidized form of TXA2 and
is excreted in urine. AT is a physiological anticoagulant.
20. C Gray syndrome is a PLT granule defect associated with a decrease in alpha granules
resulting in decreased production of alpha granule proteins, such as PF4 and beta
thromboglobulin. Alpha granule deficiency results in the appearance of agranular PLTs
when viewed in a Wright-stained blood smear.
21. D The VerifyNow P2Y12 test is used to assess a patient’s response to antiplatelet drugs,
such as clopidogrel (Plavix) and prasugrel (Effient). These drugs are given orally along
with aspirin for prevention of thrombosis or as alternative antiplatelet drugs for
patients who cannot tolerate or are not sensitive to aspirin. Clopidogrel and prasugrel
prevent PLT aggregation by irreversibly binding to P2Y12, which is a PLT membrane
receptor for ADP. The VerifyNow P2Y12 test is a whole blood test and uses ADP as
an aggregating agent to measure the level of PLT aggregation impaired by these
medications. The baseline value for PLT aggregation is established. The percent (%)
change from baseline aggregation is calculated and reported as % P2Y12 inhibition.

22. Which of the following instruments can be used to evaluate PLT function?
A. PLT aggregometer
B. VerifyNow
C. PFA-100
D. All of the above
Hemostasis/Selected methods/Reagents/Special tests/2
23. Which of the following PLT aggregating agents demonstrates a monophasic
aggregation curve when used in the optimal concentration?
A. Thrombin
B. Collagen
C. ADP
D. EPI
Hemostasis/Apply knowledge of fundamental biological characteristics/Aggregating agents/1

Answers to Questions 22–23

22. D All of the instruments listed can be used to evaluate PLT function. PLT function
testing is done either to determine the cause of bleeding in a patient with normal PLT
count and normal coagulation tests or to assess the efficacy of antiplatelet drugs. PLT
aggregometry is used for the diagnosis of inherited PLT disorders. A PLT
aggregometer uses PLT-rich plasma to measure PLT aggregation in response to
different PLT aggregating agents by measuring light transmission. A Lumi-
aggregometer uses whole blood and has the ability to measure dense-granule secretion
(by using a luminescent marker) in addition to PLT aggregation. The VerifyNow
measures a patient’s response to multiple antiplatelet drugs, including aspirin, P2Y12
inhibitors, and glycoprotein IIb/IIIa inhibitors. The Platelet Function Ananlyzer-100
 (PFA-100) is used as a screening tool for PLT function, and has replaced the bleeding
time test. It uses citrated whole blood and two cartridges. Whole blood (800 μL) is put
into each test cartridge. Vacuum is used to move the blood through a very thin glass
tube that has been coated with a membrane containing collagen and either EPI or ADP.
This coating activates the PLTs in the moving sample and promotes PLT adhesion and
aggregation. The time it takes for the clot to form inside the glass tube and prevent
further flow is measured as the closure time (CT). Initial screening is done with
collagen/EPI. If CT is normal, it is unlikely that PLT dysfunction exists. The
collagen/ADP membrane is used to confirm an abnormal collagen/EPI test result. If
both tests show abnormal results, it is likely that the patient has a PLT dysfunction, and
further testing for inherited and acquired bleeding disorders is indicated. If
collagen/ADP is normal, then the abnormal collagen/EPI test result is likely caused by
aspirin sensitivity.
23. B Collagen is the only commonly used agent that demonstrates a single-wave
(monophasic) response preceded by a lag time.
 2.3
Coagulation System Disorders
1. The APTT is sensitive to a deficiency of which clotting factor?
A. Factor VII
B. Factor X
C. PF3
D. Calcium
Hemostasis/Evaluate laboratory data to recognize health and disease states/Factor
deficiency/2
2. Which test result would be normal in a patient with dysfibrinogenemia?
A. TT
B. APTT
C. PT
D. Immunologic fibrinogen level
Hemostasis/Correlate clinical and laboratory data/Factor deficiency/2
3. A patient with a prolonged PT is given intravenous vitamin K. PT is corrected to normal
after 24 hours. Which clinical condition most likely caused these results?
A. Necrotic liver disease
B. Factor X deficiency
C. Fibrinogen deficiency
D. Obstructive jaundice
Hemostasis/Correlate clinical and laboratory data/Vitamin K deficiency/3
4. Which factor deficiency is associated with prolonged PT and APTT?
A. Factor X
B. Factor VIII
C. Factor IX
D. Factor XI
Hemostasis/Evaluate laboratory data to recognize health and disease states/Factor
deficiency/2
5. Prolonged APTT is corrected with factor VIII–deficient plasma but not with factor IX–
deficient plasma. Which factor is deficient?
A. Factor V
B. Factor VIII
C. Factor IX
D. Factor X
Hemostasis/Evaluate laboratory data to recognize health and disease states/Factor
deficiency/3
6. Which of the following is a characteristic of classic hemophilia A?
A. Abnormal PLT aggregation
B. Autosomal recessive inheritance
 C. Mild to severe bleeding episodes
D. Prolonged PT
Hemostasis/Correlate clinical and laboratory data/Hemostasis/Hemophilia/2

Answers to Questions 1–6

1. B The APTT is sensitive to the deficiency of coagulation factors in the intrinsic pathway
(factors XII, XI, IX, and VIII) and the common pathway (factors X, V, II, and I).
2. D The level of plasma fibrinogen determined immunologically is normal. In a patient
with dysfibrinogenemia, fibrinogen is not polymerized properly, causing abnormal
results of the fibrinogen-dependent coagulation tests.
3. D Obstructive jaundice contributes to coagulation disorders by preventing vitamin K
absorption. Vitamin K is fat soluble and requires bile salts for absorption. Parenteral
administration of vitamin K bypasses the bowel, hence the need for bile salts.
4. A Factor X, a common pathway factor deficiency, is most likely suspected because both
PT and APTT are prolonged. Other causes may include liver disease, vitamin K
deficiency, and anticoagulant drugs, such as warfarin and heparin.
5. C Because prolonged APTT is not corrected with factor IX–deficient plasma, factor IX is
suspected to be deficient in the test plasma.
6. C Hemophilia A (factor VIII deficiency) is characterized by mild to severe bleeding
episodes, depending on the concentration of factor VIII:C. Hemophilia A is inherited
as a sex-linked disease. PLT aggregation and PT are both normal in hemophilia A.

7. Refer to the following results:

PT = prolonged
APTT = prolonged
PLT count = decreased
Which disorder may be indicated?
A. Factor VIII deficiency
B. von Willebrand disease
C. DIC
D. Factor IX deficiency
Hemostasis/Correlate clinical and laboratory data/Coagulation disorders/3
8. Which of the following is a predisposing condition for the development of DIC?
A. Adenocarcinoma
B. Idiopathic thrombocytopenic purpura (ITP)
C. Post transfusion purpura (PTP)
D. Heparin-induced thrombocytopenia (HIT)
Hemostasis/Correlate clinical and laboratory data/DIC/1
9. Factor XII deficiency is associated with:
A. Bleeding episodes
B. Epistaxis
C. Decreased risk of thrombosis
D. Increased risk of thrombosis
 Hemostasis/Apply knowledge of fundamental biological characteristics/Factor deficiency/2
10. The following results were obtained on a patient: normal PLT count and function,
normal PT, and prolonged APTT. Which of the following disorders is most consistent
with these results?
A. Hemophilia A
B. Bernard–Soulier syndrome
C. von Willebrand disease
D. Glanzmann thrombasthenia
Hemostasis/Correlate clinical and laboratory data/Coagulation disorders/3
11. The following laboratory results were obtained from a 40-year-old woman: PT = 20 sec;
APTT = 50 sec; TT = 18 sec. What is the most probable diagnosis?
A. Factor VII deficiency
B. Factor VIII deficiency
C. Factor X deficiency
D. Hypofibrinogenemia
Hemostasis/Correlate clinical and laboratory data/Factor deficiency/3
12. When performing a factor VIII activity assay, a patient’s plasma is mixed with:
A. Normal patient plasma
B. Factor VIII–deficient plasma
C. Plasma with a high concentration of factor VIII
D. Normal control plasma
Hemostasis/Apply principles of basic laboratory procedures/Factor assay/2

Answers to Questions 7–12

7. C In DIC, there is a diffuse intravascular generation of thrombin and fibrin. As a result,
clotting factors and PLTs are consumed, resulting in decreased PLT count and
increased PT and APTT.
8. A Adenocarcinoma can liberate procoagulant (thromboplastic) substances that can
activate prothrombin intravascularly. ITP is a thrombocytopenia caused by an
autoantibody; PTP is an alloimmune thrombocytopenia caused by transfusion of blood
or blood products; HIT results from an antibody to heparin–PF4 complex causing
thrombocytopenia in 1% to 5% of patients who are on heparin therapy. In some
affected persons, thrombosis may also occur.
9. D Factor XII–deficient patients commonly have thrombotic episodes. In vitro, activated
factor XII (XIIa) activates factor XI to factor XIa. In vivo, however, factor XII plays a
major role in the fibrinolytic system by activating plasminogen to form plasmin.
Hemorrhagic manifestations are not associated with factor XII deficiency because
VIIa/TF can activate factor IX to factor IXa and factor X to factor Xa to generate
thrombin.
10. A Hemophilia A is associated with deficiency of factor VIII, resulting in bleeding and
abnormal APTT. The PLT number and function are normal in this disorder. Von
Willebrand disease is a disorder of PLT adhesion associated with decreased VWF and
factor VIII, causing an abnormal PLT function test result and abnormal APTT. Both
 Glanzmann thrombasthenia and Bernard–Soulier syndrome cause abnormal PLT
aggregation but do not cause abnormal APTT.
11. D Fibrinogen (factor I) is a clotting protein of the common pathway and is evaluated by
TT. In hypofibrinogenemia (fibrinogen concentration less than 100 mg/dL), PT, APTT,
and TT are prolonged. In factor VII deficiency, APTT is normal; in factor VIII
deficiency, PT is normal; and in factor X deficiency, TT is normal.
12. B Coagulation factor assays are based on the ability of the patient’s plasma to correct
any specific factor–deficient plasma. To measure for factor VIII activity in a patient’s
plasma, diluted patient plasma is mixed with factor VIII–deficient plasma. The APTT
test is performed on the mixture. Each laboratory should calculate its own normal
ranges, which are based on the patient population, reagents, and instrument used. A
range of 50% to 150% is considered normal.

13. The most suitable product for treatment of factor VIII deficiency is:
A. Fresh frozen plasma (FFP)
B. Factor VIII concentrate
C. Prothrombin complex concentrate
D. Factor V Leiden
Hemostasis/Correlate clinical and laboratory data/Treatment/2
14. Which of the following is associated with an abnormal PLT aggregation test result?
A. Factor VIII deficiency
B. Factor VIII inhibitor
C. Lupus anticoagulant
D. Afibrinogenemia
Hemostasis/Correlate clinical and laboratory data/Factor deficiency/2
15. Refer to the following results:
PT = normal
APTT = prolonged
PLT count = normal
PLT aggregation to ristocetin = abnormal
Which of the following disorders may be indicated?
A. Factor VIII deficiency
B. DIC
C. von Willebrand disease
D. Factor IX deficiency
Hemostasis/Correlate clinical and laboratory data/Coagulation disorders/3
16. Which results are associated with hemophilia A?
A. Prolonged APTT, normal PT
B. Prolonged PT and APTT
C. Prolonged PT, normal APTT
D. Normal PT and APTT
Hemostasis/Correlate clinical and laboratory data/Hemophilia/2
17. Fibrin monomers are increased in which of the following conditions?
A. Primary fibrinolysis
B. DIC
 C. Factor VIII deficiency
D. Fibrinogen deficiency
Hemostasis/Correlate clinical and laboratory data/2
18. Which of the following is associated with multiple factor deficiencies?
A. An inherited disorder of coagulation
B. Severe liver disease
C. Dysfibrinogenemia
D. Lupus anticoagulant
Hemostasis/Correlate clinical and laboratory data/Factor deficiency/2
19. Normal PT and APTT results in a patient with poor wound healing may be associated
with:
A. Factor VII deficiency
B. Factor VIII deficiency
C. Factor XII deficiency
D. Factor XIII deficiency
Hemostasis/Correlate clinical and laboratory data/Factor deficiency/2

Answers to Questions 13–19

13. B Factor VIII concentrate (human or recombinant) is the treatment of choice for patients
with factor VIII deficiency. FFP contains factor VIII; however, it is no longer used as
the primary treatment for factor VIII deficiency. Prothrombin complex concentrate is
used to treat patients with factor VIII inhibitor.
14. D Fibrinogen is a plasma protein that is essential for PLT aggregation as well as fibrin
formation. In afibrinogenemia, PLT aggregation is abnormal.
15. C VWF is involved in both PLT adhesion and coagulation via complexing with factor
VIII. Therefore, in von Willebrand disease (deficiency or functional abnormality of
VWF) factor VIII is also decreased, causing abnormal APTT as well as abnormal PLT
aggregation to ristocetin. The PLT count and PT are not affected in VWF deficiency.
16. A Hemophilia A is associated with factor VIII deficiency. Factor VIII is a factor in the
intrinsic coagulation pathway that is evaluated by the APTT test and not the PT test.
The PT test evaluates the extrinsic and common pathways.
17. B Increased fibrin monomers result from coagulation activation. DIC is an acquired
condition associated with spontaneous activation of coagulation and fibrinolysis. In
primary fibrinolysis, the fibrinolytic system is activated, and fibrin monomers are
normal.
18. B Most of the clotting factors are made in the liver. Therefore, severe liver disease
results in multiple-factor deficiencies. An inherited disorder of coagulation is
commonly associated with a single-factor deficiency. Lupus anticoagulant is directed
against the phospholipid-dependent coagulation factors. Dysfibrinogenemia results
from an abnormal fibrinogen molecule.
19. D Factor XIII deficiency can lead to impaired wound healing and may cause severe
bleeding problems. Factor XIII is a fibrin stabilizing factor that changes the fibrinogen
 bonds in fibrin polymers to stable covalent bonds. Factor XIII is not involved in the
process of fibrin formation and, therefore, PT and APTT are both normal.

20. Fletcher factor (prekallikrein) deficiency may be associated with:

A. Bleeding
B. Thrombosis
C. Thrombocytopenia
D. Thrombocytosis
Hemostasis/Correlate clinical and laboratory data/Factor deficiency/2
21. One of the complications associated with a severe hemophilia A is:
A. Hemarthrosis
B. Mucous membrane bleeding
C. Mild bleeding during surgery
D. Immune-mediated thrombocytopenia
Hemostasis/Apply knowledge of fundamental biological characteristics/Hemophilia/1
22. The most common subtype of classic von Willebrand disease is:
A. Type 1
B. Type 2A
C. Type 2B
D. Type 3
Hemostasis/Apply knowledge of fundamental biological characteristics/von Willebrand
disease/2
23. Prolonged APTT and PT are corrected when mixed with normal plasma. Which factor
is most likely deficient?
A. Factor VIII
B. Factor V
C. Factor XI
D. Factor IX
Hemostasis/Evaluate laboratory data to recognize health and disease states/Factor
deficiency/3

Answers to Questions 20–23

20. B Fletcher factor (prekallikrein) is referred to as a contact factor. Activated prekallikrein
is named kallikrein. In vitro, kallikrein is involved in activation of factor XI to XIa
causing prolonged APTT. In vivo, it plays a role in the fibrinolytic system and, similar
to factor XII deficiency, Fletcher factor deficiency may be associated with thrombosis.
21. A In severe hemophilia A, factor VIII activity is less than 1%, resulting in a severe
bleeding diathesis, such as hemarthrosis (bleeding into the joints).
22. A VWF is a multimeric plasma glycoprotein that results in different subtypes of von
Willebrand disease with varied severity. The most common subtype is subtype 1, and
70% to 80% of these cases are associated with mild bleeding. Subtype 3 involves the
total absence of the von Willebrand molecule and is associated with severe bleeding.
Subtypes 2A and 2B result in deficiency of intermediate- and/or high-molecular-
weight portions of the von Willebrand molecule and are associated with 10% to 12%
 and 3% to 6% of cases of von Willebrand disease, respectively.
23. B Factor V (common pathway factor) deficiency is most likely suspected because both
PT and APTT are prolonged, and both are corrected when mixed with normal plasma.
 2.4
Inhibitors, Thrombotic Disorders, and Anticoagulant
Drugs
1. Which characteristic describes antithrombin (AT)?
A. It is synthesized in megakaryocytes
B. It is activated by protein C
C. It is a cofactor of heparin
D. It is a pathological inhibitor of coagulation
Hemostasis/Apply knowledge of fundamental biological characteristics/AT/1
2. Which laboratory test is affected by heparin therapy?
A. Thrombin time
B. Fibrinogen assay
C. Protein C assay
D. Protein S assay
Hemostasis/Apply knowledge of fundamental biological
characteristics/Hemostasis/Heparin/2
3. Abnormal APTT caused by a pathological circulating anticoagulant is:
A. Corrected with factor VIII–deficient plasma
B. Corrected with factor IX–deficient plasma
C. Corrected with normal plasma
D. Not corrected with normal plasma
Hemostasis/Correlate clinical and laboratory data/Special tests/2
4. The lupus anticoagulant affects which of the following tests?
A. Factor VIII assay
B. Factor IX assay
C. VWF assay
D. Phospholipid-dependent assays
Hemostasis/Apply knowledge of fundamental biological characteristics/Lupus
anticoagulant/2
5. Which statement about warfarin (Coumadin) is accurate?
A. It is a vitamin B antagonist
B. It is not recommended for pregnant and lactating women
C. It needs AT as a cofactor
D. APTT test is used to monitor its dosage
Hemostasis/Apply knowledge of fundamental biological characteristics/Warfarin/2

Answers to Questions 1–5

1. C AT is a heparin cofactor and is the most important naturally occurring physiological
 inhibitor of blood coagulation. It represents about 75% of antithrombotic activity and
is an α2-globulin made by the liver.
2. A Heparin is an AT drug and therefore increases TT along with APTT and PT. Heparin
therapy has no effect on fibrinogen, protein C, or protein S assays.
3. D In the presence of a pathological circulating anticoagulant, a mixing test using normal
plasma does not correct abnormal APTT. These anticoagulants are pathological
substances and are endogenously produced. They are either directed against a specific
clotting factor or against a group of factors. Prolonged APTT caused by a factor
deficiency is corrected when mixed with normal plasma. Factors VIII– and factor IX–
deficient plasmas are used for assaying the activities of factors VIII and IX,
respectively.
4. D The lupus anticoagulant interferes with phospholipid-dependent coagulation assays,
such as the PT and APTT tests. The lupus anticoagulant does not inhibit clotting factor
assays and does not inhibit in vivo coagulation.
5. B Warfarin (Coumadin) crosses the placenta and is present in human milk; it is not
recommended for pregnant and lactating women. Warfarin is a vitamin K antagonist
drug that retards synthesis of the active form of vitamin K–dependent factors (II, VII,
IX, and X). AT is a heparin (not warfarin) cofactor. The INR is used to monitor
warfarin dosage.

6. Which statement regarding protein C is correct?

A. It is a vitamin K–independent zymogen
B. It is activated by fibrinogen
C. It activates cofactors V and VIII
D. Its activity is enhanced by protein S
Hemostasis/Apply knowledge of fundamental biological characteristics/Protein C/1
7. Which of the following is an appropriate screening test for the diagnosis of lupus
anticoagulant?
A. Thrombin time
B. Diluted Russell viper venom test (DRVVT)
C. D-dimer test
D. Fibrinogen assay
Hemostasis/Correlate clinical and laboratory data/Lupus anticoagulant/2
8. Which of the following is most commonly associated with activated protein C resistance
(APCR)?
A. Bleeding
B. Thrombosis
C. Epistaxis
D. Menorrhagia
Hemostasis/Correlate clinical and laboratory data/APCR/2
9. A 50-year-old man has been on heparin for the past 7 days. Which combination of tests
is expected to be abnormal?
A. PT and APTT only
B. APTT, TT only
 C. APTT, TT, fibrinogen assay
D. PT, APTT, TT
Hemostasis/Correlate clinical and laboratory data/Heparin therapy/3
10. Which of the following drugs inhibits ADP-mediated PLT aggregation?
A. Heparin
B. Warfarin
C. Aspirin
D. Prasugrel
Hemostasis/Correlate clinical and laboratory data/Therapies/2
11. Thrombin–TM complex is necessary for activation of:
A. Protein C
B. AT
C. Protein S
D. Factors V and VIII
Hemostasis/Apply knowledge of fundamental biological characteristics/Thrombomodulin/2

Answers to Questions 6–11

6. D Protein S functions as a cofactor of protein C and, as such, enhances its activity.
Activated protein C (APC) inactivates factors Va and VIIIa.
7. B Russell viper venom (RVV) reagent contains factors X and V, activating enzymes that
are strongly phospholipid dependent. The reagent also contains RVV, Ca2+, and
phospholipid. In the presence of phospholipid autoantibodies, such as lupus
anticoagulant, the reagent phospholipid is partially neutralized, causing prolongation of
clotting time. TT evaluates fibrinogen. D-dimer tests evaluate fibrin degradation
products. Fibrinogen assay and TT are not indicated for the diagnosis of lupus
anticoagulant.
8. B APCR is the single most common cause of inherited thrombosis. In 90% of individuals,
the cause is gene mutation of factor V (factor V Leiden). Affected individuals are
predisposed to thrombosis, mainly after age 40 years. Heterozygous individuals may
not manifest thrombosis unless other clinical conditions coexist.
9. D Heparin is a therapeutic anticoagulant with an AT activity. Heparin also inhibits factors
XIIa, XIa, Xa, and IXa. In patients receiving heparin therapy, PT, APTT, and TT are
all prolonged. Quantitative fibrinogen assay, however, is not affected by heparin
therapy.
10. D Prasugrel (Effient) is an antiplatelet drug that reduces PLT aggregation by irreversibly
blocking P2Y12 receptors on the PLT surface membrane, thereby inhibiting PLT
aggregation to ADP. Aspirin is another antiplatelet drug that inhibits PLT aggregation
by blocking the action of the enzyme cyclo-oxygenase. Warfarin and heparin are
anticoagulant drugs that act against clotting factors.

11. A Protein C is activated by thrombin–TM complex. TM is a transmembrane protein that

accelerates protein C activation 1,000-fold by forming a complex with thrombin. When
thrombin binds to TM, it loses its clotting function, including activation of factors V and
 VIII. APC deactivates factors Va and VIIIa. Protein S is a cofactor necessary for the
activation of protein C.
12. Which test is used to monitor heparin therapy?
A. INR
B. Chromogenic anti–factor Xa assay
C. TT
D. PT
Hemostasis/Correlate clinical and laboratory data/Heparin therapy/2
13. Which test is commonly used to monitor warfarin therapy?
A. INR
B. APTT
C. TT
D. Ecarin time
Hemostasis/Correlate clinical and laboratory data/Warfarin therapy/2
14. Which clotting factors (cofactors) are inhibited by protein S?
A. Factors V and X
B. Factors Va and VIIIa
C. Factors VIII and IX
D. Factors VIII and X
Hemostasis/Correlate clinical and laboratory data/Clotting factors/2
15. Which drug promotes fibrinolysis?
A. Warfarin
B. Heparin
C. Urokinase
D. Aspirin
Hemostasis/Correlate clinical and laboratory data/Therapies/2
16. Diagnosis of lupus anticoagulant is confirmed by which of the following criteria?
A. Decreased APTT
B. Correction of APPT by mixing studies
C. Neutralization of the antibody by high concentration of phospholipids
D. Confirmation that abnormal coagulation tests are related to factor deficiencies
Hemostasis/Correlate clinical and laboratory data/LA/3
17. Which of the following abnormalities is consistent with the presence of lupus
anticoagulant?
A. Decreased APTT/bleeding complications
B. Prolonged APTT/thrombosis
C. Prolonged APTT/thrombocytosis
D. Thrombocytosis/thrombosis
Hemostasis/Correlate clinical and laboratory data/LA/3

Answers to Questions 12–17

12. B Heparin dosage can be best monitored by the chromogenic anti–factor Xa assay. In
anti–factor Xa assay, the concentration of heparin is determined by inhibition of factor
Xa by AT. Anti–factor Xa assay uses a reagent with a fixed concentration of factor Xa
 and AT. Heparin forms a complex with AT and factor Xa reagents. Excess factor Xa
combines with the chromogenic substrate to form a colored product; the color intensity
is inversely proportional to the concentration of heparin. PT would be prolonged in
heparin therapy, but the PT test is not sensitive enough to be used to monitor heparin
therapy. Heparin inhibits thrombin and, therefore, causes prolonged TT. The TT test,
however, is not used to monitor heparin therapy either.
13. A Warfarin is a vitamin K–antagonist drug. It inhibits vitamin K–dependent factors (II,
VII, IX, and X) and other vitamin K–dependent proteins, such as proteins C and S.
Warfarin therapy is monitored with the INR. An INR of 2.0 to 3.0 is used as the target
when monitoring warfarin therapy for prophylaxis and treatment of deep vein
thrombosis (DVT). A higher dose of warfarin (giving an INR of 2.5–3.5) is required
for patients with mechanical heart valves.
14. B Factors Va and VIIIa are deactivated by protein S and activated by protein C.
15. C Urokinase is a thrombolytic drug that can be used to treat acute arterial thrombosis.
Urokinase can also be used for the treatment of venous thromboembolism, myocardial
infarction, and clotted catheters. Warfarin and heparin are anticoagulant drugs, whereas
aspirin prevents PLT aggregation by inhibiting cyclo-oxygenase.
16. C The International Society of Hemostasis and Thrombosis has recommended four
criteria for the diagnosis of lupus anticoagulant: (1) prolongation of one or more of the
phospholipid-dependent clotting tests, such as APTT or DRVVT; (2) presence of an
inhibitor confirmed by mixing studies (not corrected); (3) evidence that the inhibitor is
directed against phospholipids by neutralizing the antibodies with a high concentration
of phospholipids (PLT neutralization test or DRVVT with platelet rich plasma or
confirming phospholipid reagent); and (4) lack of any other causes for thrombosis.
17. B Lupus anticoagulant interferes with phospholipids in the APTT reagent, resulting in
prolongation of APTT. However, in vivo, lupus anticoagulant decreases fibrinolytic
activity, causing an increased risk of thrombosis. Lupus anticoagulant does not result
in a bleeding tendency unless there is a coexisting thrombocytopenia or other
coagulation abnormality.

18. Which of the following is a characteristic of LMWH?

A. Generally requires monitoring
B. Specifically acts on factor Va
C. Has a longer half-life compared with unfractionated heparin (UFH)
D. Can be used as a fibrinolytic agent
Hemostasis/Apply knowledge of fundamental biological characteristics/LMWH/1
19. Which of the following tests is most likely to be abnormal in patients taking aspirin?
A. PLT morphology
B. PLT count
C. PLT aggregation
D. PT
Hemostasis/Correlate clinical and laboratory data/Aspirin therapy/2
20. Which of the following is associated with AT deficiency?
A. Thrombocytosis
 B. Thrombosis
C. Thrombocytopenia
D. Bleeding
Hemostasis/Correlate clinical and laboratory data/Inhibitors/2
21. Which of the following may be associated with thrombotic events?
A. Decreased protein C
B. Increased fibrinolysis
C. Afibrinogenemia
D. Idiopathic thrombocytopenic purpura
Hemostasis/Correlate clinical and laboratory data/Protein C/2
22. Aspirin resistance may be associated with:
A. Bleeding
B. Factor VIII deficiency
C. Thrombosis
D. Thrombocytosis
Hemostasis/Correlate clinical and laboratory data/Aspirin resistance/2
23. Prolonged TT is indicative of which of the following antithrombotic agents?
A. Prasugrel
B. Clopidogrel
C. Aspirin
D. Heparin
Hemostasis/Correlate clinical and laboratory data/Antithrombotic therapy/2
24. Screening tests for thrombophilia should be performed on:
A. All pregnant women because of the risk of thrombosis
B. Patients with a negative family history
C. Patients with thrombotic events occurring at a young age
D. Patients who are receiving anticoagulant therapy
Hemostasis/Correlate clinical and laboratory data/Thrombophilia/2

Answers to Questions 18–24

18. C LMWH is a small glycosaminoglycan that is derived from UFH. LMWH has a low
affinity for plasma proteins and endothelial cells and therefore has a longer half-life.
The half-life of the drug does not depend on the dosage. LMWH has an inhibitory
effect on factors Xa and IIa. It does not require routine monitoring except in patients
with renal failure, obese patients, pediatric patients, and pregnant patients.
19. C Aspirin is an antiplatelet drug. It prevents PLT aggregation by inhibition of cyclo-
oxygenase. Aspirin has no effect on the PLT count, PLT morphology, or PT.
20. B AT is a physiological anticoagulant. It inhibits factors IIa, Xa, IXa, XIa, and XIIa.
Deficiency of AT is associated with thrombosis. Thrombotic events commonly occur
when AT deficiency is associated with another risk factor, such as pregnancy, surgery,
or an inherited thrombotic disorder (e.g., factor V Leiden).
21. A Protein C is a physiological inhibitor of coagulation. It is activated by thrombin–TM
complex. APC inhibits cofactors Va and VIIIa. Protein C deficiency is associated with
 thrombosis. Increased fibrinolysis, afibrinogenemia, and ITP are associated with
bleeding.
22. C Up to 22% of patients taking aspirin become resistant to aspirin’s antiplatelet effect.
Patients who are aspirin resistant have a higher risk of thrombosis (heart attacks and
strokes).
23. D Heparin is an AT drug causing prolonged TT in patients who are on heparin therapy.
Prasugrel, clopidogrel, and aspirin are antiplatelet drugs causing inhibition of PLT
aggregation.
24. C Laboratory tests for evaluation of thrombophilia are justified in young patients with
thrombotic events, in patients with a positive family history after a single thrombotic
event, in those with recurrent spontaneous thrombosis, and in pregnancies associated
with thrombosis.

25. Prothrombin G20210A is characterized by which of the following causes and

conditions?
A. Single mutation of prothrombin molecule/bleeding
B. Single mutation of prothrombin molecule/thrombosis
C. Decreased levels of prothrombin in plasma/thrombosis
D. Increased levels of prothrombin in plasma/bleeding
Hemostasis/Correlate clinical and laboratory data/Prothrombin/2
26. Factor V Leiden promotes thrombosis by preventing:
A. Inactivation of factor Va
B. Activation of factor V
C. Activation of protein C
D. Activation of protein S
Hemostasis/Correlate clinical and laboratory data/Factor V Leiden/2
27. What is the approximate incidence of antiphospholipid antibodies in the general
population?
A. Less than 1%
B. 1%–2%
C. 3%–8%
D. 10%–15%
Hemostasis/Apply knowledge of fundamental biological characteristics/LA/1
28. Which of the following laboratory tests is helpful in the diagnosis of aspirin resistance?
A. APTT
B. PT
C. PLT count and morphology
D. PLT aggregation
Hemostasis/Correlate clinical and laboratory data/Aspirin resistance/2
29. Which of the following complications may occur as a result of decreased tissue factor
pathway inhibitor (TFPI)?
A. Increased episodes of hemorrhage
B. Increased risk of thrombosis
C. Impaired PLT plug formation
 D. Immune thrombocytopenia
Hemostasis/Apply knowledge of fundamental biological characteristics/TFPI/2
30. Factor VIII inhibitors occur in __________ of patients with factor VIII deficiency.
A. 40%–50%
B. 30%–40%
C. 25%–30%
D. 20%–25%
Hemostasis/Apply knowledge of fundamental biological characteristics/Inhibitors/1

Answers to Questions 25–30

25. B Prothrombin G20210A is defined as a single-point mutation of the prothrombin gene,
resulting in increased concentration of plasma prothrombin and, thus, is a risk factor
for thrombosis. Prothrombin G20210A is the second most common cause of inherited
hypercoagulability (after factor V Leiden). It has the highest incidence in white people
from southern Europe. The thrombotic episodes generally occur before age 40 years.
26. A Factor V Leiden is a single-point mutation in the factor V gene that inhibits factor Va
inactivation by protein C. APC enhances deactivation of factors Va and VIIIa.
27. B The incidence of antiphospholipid antibodies in the general population is about 1% to
2%.
28. D Currently, the PLT aggregation test is considered the gold standard for evaluation of
aspirin resistance. In aspirin resistance, PLT aggregation is not inhibited by aspirin
ingestion. Aspirin resistance has no effect on PLT count and morphology.
29. B TFPI is released from the vasculature and is the most important inhibitor of the
extrinsic pathway. TFPI inhibits factors Xa and VIIa–TF complex. Therefore, the
deficiency of TFPI is associated with thrombosis.
30. D Factor VIII inhibitors (alloantibodies) occur in 20% to 25% of patients who have
factor VIII deficiency and are receiving factor VIII replacement.

31. Which therapy and resulting mode of action are appropriate for the treatment of a
patient with a high titer of factor VIII inhibitors?
A. Factor VIII concentrate to neutralize the antibodies
B. Recombinant factor VIIa (rVIIa) to activate factor X
C. Factor X concentrate to activate the common pathway
D. FFP to replace factor VIII
Hemostasis/Apply knowledge of fundamental biological characteristics/Inhibitors/2
32. The Bethesda assay is used for which determination?
A. Lupus anticoagulant titer
B. Factor VIII inhibitor titer
C. Factor V Leiden titer
D. Protein S deficiency
Hemostasis/Select methods/Reagents/Special tests/2
33. Hyperhomocysteinemia may be a risk factor for:
A. Bleeding
 B. Thrombocythemia
C. Thrombosis
D. Thrombocytopenia
Hemostasis/Correlate clinical and laboratory data/Homocysteinemia/2
34. Which drug may be associated with DVT?
A. Aspirin
B. tPA
C. Oral contraceptives
D. Clopidogrel (Plavix)
Hemostasis/Apply knowledge of fundamental biological characteristics/Thrombosis/2
35. Argatroban may be used as an anticoagulant drug in patients with:
A. DVT
B. Hemorrhage
C. TTP
D. Thrombocytosis
Hemostasis/Apply knowledge of fundamental biological characteristics/Therapies/2
36. Heparin-induced thrombocytopenia (HIT) results from:
A. Antibodies to heparin
B. Antibodies to PLTs
C. Antibodies to PF4
D. Antibodies to heparin–PF4 complex
Hemostasis/Apply knowledge of fundamental biological characteristics/HIT/2

Answers to Questions 31–36

31. B rVIIa is effective for the treatment of a high-titer factor VIII inhibitor. Factor VIIa can
directly activate factor X to factor Xa in the absence of factors VIII and IX. rVIIa does
not stimulate anamnestic responses in patients with factor VIII inhibitor. Factor VIII
concentrate is used for a low-titer factor VIII inhibitor. Factor X concentrate and FFP
are not the treatments of choice for factor VIII inhibitor.
32. B The Bethesda assay is a quantitative assay for factor VIII inhibitor. In this assay,
normal plasma is incubated with different dilutions of the patient’s plasma or with a
normal control. The inhibitor inactivates factor VIII present in normal plasma
following incubation for 2 hours at 37°C. The residual activities in the sample are
determined, and the inhibitor titer is calculated.
33. C Elevated plasma homocysteine is a risk factor for the development of DVT, coronary
heart disease and stroke. Homocystinemia may be inherited or acquired. Acquired
homocystinemia is caused by dietary deficiencies of vitamins B6, B12, and folic acid.
34. C Oral contraceptive drugs are acquired risk factors for thrombosis. Aspirin and
clopidogrel are antiplatelet drugs, and tPA is a fibrinolytic drug used for the treatment
of thrombosis.
35. A Argatroban is a direct thrombin-inhibiting drug and may be used as an anticoagulant
in patients with HIT to prevent thrombosis. Argatroban is a small synthetic molecule
that binds to free and clot-bound thrombin. Argatroban affects TT, PT, APTT, and
 activated clotting time (ACT) tests. The APTT test is recommended for monitoring the
dosage with the target therapeutic range of 1.5 to 3.0 times the mean of the laboratory
reference range. In patients with lupus anticoagulant or factor deficiencies, baseline
APTT is prolonged; in these conditions, Ecarin time can be used as an alternative
assay.
36. D HIT is an immune process caused by the production of antibodies to heparin–PF4
complex. This immune complex binds to PLT Fc receptors, causing PLT activation
and formation of PLT microparticles, which, in turn, induce hypercoagulability and
thrombocytopenia.

37. Which laboratory test is used to screen for APCR?

A. Mixing studies with normal plasma
B. Mixing studies with factor-deficient plasma
C. Modified APTT with and without APC
D. Modified PT with and without APC
Hemostasis/Select methods/Reagents/Special tests/2
38. Ecarin clotting time may be used to monitor:
A. Heparin therapy
B. Warfarin therapy
C. Fibrinolytic therapy
D. Bivalirudin
Hemostasis/Select methods/Reagents/Special tests/2
39. Which of the following may interfere with the APCR screening test?
A. Lupus anticoagulant
B. Protein C deficiency
C. AT deficiency
D. Protein S deficiency
Hemostasis/Correlate clinical and laboratory/Special tests/2
40. Thrombophilia may be associated with which of the following disorders?
A. Afibrinogenemia
B. Hypofibrinogenemia
C. Factor VIII inhibitor
D. Hyperfibrinogenemia
Hemostasis/Apply knowledge of fundamental biological characteristics/Fibrinogen/2
41. Which of the following anticoagulant drugs can be used in patients with HIT?
A. Warfarin
B. Heparin
C. Aspirin
D. Argatroban
Hemostasis/Apply knowledge of fundamental biological characteristics/Therapies/2

Answers to Questions 37–41

37. C APCR can be evaluated by performing a two-part APTT test. The APTT is measured
on the patient’s plasma with and without the addition of APC. The result is expressed
 as the ratio of the APTT with APC to the APTT without APC. The normal ratio is 2:5.
Patients with APCR have a lower ratio than the reference range. A positive screening
test should be followed by a confirmatory test, such as polymerase chain reaction
(PCR) for factor V Leiden.
38. D Ecarin clotting time, a snake venom–based clotting assay, may be used to monitor
bivalirudin therapy in instances when the baseline APTT is prolonged as a result of
lupus anticoagulant or factor deficiencies. Heparin therapy is monitored by using the
anti–factor Xa assay; warfarin therapy is monitored with the INR. Fibrinolytic therapy
may be monitored by using the D-dimer test.
39. A The lupus anticoagulant interferes with the APCR screening assay based on the APTT
ratio with and without the addition of APC. Persons with the lupus anticoagulant have
a prolonged APTT that renders the test invalid for APCR screening.
40. D Hyperfibrinogenemia is a risk factor for thrombophilia. Fibrinogen is an acute-phase
reactant and may be increased in inflammation, stress, obesity, smoking, and
medications, such as oral contraceptives. Hypofibrinogenemia, afibrinogenemia, and
factor VIII inhibitors are associated with bleeding.
41. D Argatroban is a direct thrombin inhibitor drug and used in patients with HIT who
cannot tolerate heparin or LMWH therapy. Warfarin should not be used for
anticoagulation in persons with HIT because it causes a fall in protein C concentration
and vitamin K–dependent coagulation factors. Aspirin is an antiplatelet drug.

42. Which of the following is the preferred method to monitor heparin therapy at the point
of care during cardiac surgery?
A. APTT
B. ACT
C. PT
D. TT
Hemostasis/Correlate clinical and laboratory/Special tests/2
43. Mrs. Smith has the following laboratory results and no history of bleeding:
APTT = prolonged
APTT results on a 1:1 mixture of the patient’s plasma with normal plasma:
Preincubation: prolonged APTT
2-hour incubation: prolonged APTT
These results are consistent with:
A. Factor VIII deficiency
B. Factor VIII inhibitor
C. Lupus anticoagulant
D. Protein C deficiency
Hemostasis/Correlate clinical and laboratory data/Special tests/3
44. Which test may be used to monitor LMWH therapy?
A. APTT
B. INR
 C. Anti–factor Xa heparin assay
D. ACT
Hemostasis/Correlate clinical and laboratory data/LMWH therapy/2

Answers to Questions 42–44

42. B ACT is a point-of-care coagulation test used to monitor high-dose heparin therapy
during cardiac surgery, cardiac angioplasty, hemodialysis, and other major surgeries. It
is the preferred method to determine if sufficient heparin was administered to prevent
clotting during surgery because it is more rapid than the APTT test. The test uses a clot
activator, such as kaolin or Celite, to stimulate coagulation, and the time in seconds is
linearly related to the dose of heparin administered. The ACT test is available in
different formats, and the reference range varies, depending on the method used. At
low to moderate heparin doses, the ACT test does not correlate well with the APTT
test or the anti–factor Xa assay.
43. C Mixing studies differentiate factor deficiencies from factor inhibitors. Lupus
anticoagulant is associated with thrombosis, and it is directed against phospholipid-
dependent coagulation tests, such as the APTT test. In patients with lupus
anticoagulant, after the patient’s plasma is mixed with normal plasma, APTT remains
prolonged immediately after mixing and following 2 hours of incubation. Factor VIII
deficiency and factor VIII inhibitor are associated with bleeding.
44. C The anti–factor Xa heparin assay is used to monitor LMWH therapy, when required,
because the APTT test is insensitive to LMWH. The assay can be performed by
chromogenic endpoint detection used on automated analyzers. The principle of the test
is to measure the inhibition of factor Xa by heparin. The reagent is a mixture of a fixed
concentration of factor Xa, a substrate which is specific for factor Xa, and a fixed
concentration of AT. Some kits rely on the AT in the patient’s plasma. Heparin forms a
complex with AT and factor Xa (AT–heparin–factor Xa). Excess free factor Xa cleaves
the chromogenic substrate and releases a yellow product. The color intensity of the
product is inversely proportional to plasma heparin concentration and is measured by a
photodetector at 405 nm. LMWH therapy usually does not require monitoring;
however, exceptions include pediatric, obese, and pregnant patients and those with
renal failure.
 2.5
Hemostasis Problem-Solving
1. Patient History
A 3-year-old male was admitted with scattered petechiae and epistaxis. The patient had
normal growth and had no other medical problems except for chickenpox 3 weeks
earlier. His family history was unremarkable.
Laboratory Results
Patient Reference Range
PT 11 sec 10–13 sec
APTT 32 sec 28–37 sec
PLT count 18 × 103/µL L 150–450 × 103/μL
These clinical manifestations and laboratory results are consistent with which
condition?
A. TTP
B. DIC
C. ITP
D. HUS
Hemostasis/Evaluate laboratory data to recognize health and disease states/Platelet
disorders/3

Answer to Question 1
1. C These clinical manifestations and laboratory results are consistent with ITP. ITP is an
autoimmune thrombocytopenia. In children, acute ITP occurs after a viral infection, as
was the case in this 3-year-old patient. Clinical manifestations are associated with
petechiae, purpura, and mucous membrane bleeding, such as epistaxis and gingival
bleeding. Abnormal laboratory tests include a very low PLT count, and other causes of
thrombocytopenia should be ruled out in patients with suspected ITP.

2. Patient History
A 12-year-old white male has the following symptoms: visible bruising on arms and
legs, bruising after sports activities, and excessive postoperative hemorrhage after
tonsillectomy 3 months ago. His family history revealed that his mother suffers from
heavy menstrual bleeding, and his maternal grandfather had recurrent nosebleeds and
bruising.
Laboratory Results
Patient Reference Range
 PLT count: 350 × 103/μL 200–450 × 103/μL
PT 11 sec 10–12 sec
APTT 70 sec 28–37 sec
TT 13 sec 10–15 sec
PLT AGGREGATION
Normal aggregation with collagen, EPI, ADP
Abnormal aggregation with ristocetin
CONFIRMATORY TESTS PATIENT REFERENCE RANGE
VWF:Rco 25% 45%–140%
VIII:C 20% 50%–150%
VWF:antigen 10% 45%–185%
These clinical manifestations and laboratory results are consistent with which
diagnosis?
A. Factor VIII deficiency
B. von Willebrand disease
C. Glanzmann thrombasthenia
D. Bernard-Soulier syndrome
Hemostasis/Evaluate laboratory data to recognize health and disease states/Platelet
disorders/3
3. The following results are obtained from a patient who developed severe bleeding:
Prolonged PT and APTT
PLT count = 100 × 109/L
Fibrinogen = 40 mg/dL
Which of the following blood products should be recommended for transfusion?
A. Factor VIII concentrate
B. PLTs
C. FFP
D. Cryoprecipitate
Hemostasis/Correlate clinical and laboratory data/Therapies/2
4. A 30-year-old woman develops signs and symptoms of thrombosis in her left lower leg
after 5 days of heparin therapy. The patient had had open-heart surgery 3 days
previously and has been on heparin ever since. Which of the following would be most
helpful in making the diagnosis?
A. Fibrinogen assay
B. PT
C. PLT count
D. Increased heparin dose
Hemostasis/Correlate clinical and laboratory data/Heparin therapy/3
 Answers to Questions 2–4
2. B These clinical manifestations and laboratory results are consistent with von Willebrand
disease. von Willebrand disease is an inherited bleeding disorder caused by abnormal
PLT adhesion and aggregation. In von Willebrand disease, VWF is deficient or
dysfunctional. VWF enhances the release of factor VIII from the liver, and it also
forms a complex with factor VIII in the circulation. Deficient or dysfunctional VWF
results in decreased factor VIII as well and, therefore, an increase in APTT values. The
clinical manifestations associated with von Willebrand disease are easy bruising,
epistaxis, and bleeding after surgery. The diagnostic laboratory test shows abnormal
PLT aggregation to ristocetin, which is corrected by addition of normal plasma
containing VWF. APTT is prolonged as a result of the deficiency of factor VIII. Factor
VIII activity (VIII:C), VWF ristocetin cofactor activity (VWF:Rco), and VWF:
antigenic activity (VWF:antigen) are abnormal. The PLT count and PT are normal in
von Willebrand disease.
3. D Cryoprecipitate contains fibrinogen, factor VIII, and VWF. FFP has all of the clotting
factors; however, it is not the best choice if cryoprecipitate is available.
4. C The PLT count should be checked every other day in patients receiving heparin
therapy. HIT should be suspected in patients who are not responding to heparin therapy
and/or are developing thrombocytopenia (50% below the baseline value) and
thrombotic complications while on heparin therapy. Increase in heparin dose should be
avoided in patients with the clinical symptoms of thrombosis while they are receiving
heparin. Fibrinogen assay and PT are not the appropriate assays for monitoring heparin
therapy, nor are they used to test for HIT.

5. The following laboratory results were obtained on a 25-year-old woman with

menorrhagia after delivery of her second son. The patient has no previous bleeding
history.
Normal PLT count; normal PT; prolonged APTT
Mixing of the patient’s plasma with normal plasma
corrected the prolonged APTT on immediate testing.
However, mixing followed by 2-hour incubation at 37°C
caused prolonged APTT.
What is the most probable cause of these laboratory results?
A. Lupus anticoagulant
B. Factor VIII deficiency
C. Factor IX deficiency
D. Factor VIII inhibitor
Hemostasis/Evaluate laboratory data to recognize health and disease states/Mixing studies/3
6. A 62-year-old female presents with jaundice and the following laboratory data:
Peripheral blood smear = macrocytosis, target cells
PLT count = 355 × 109/L
PT = 25 sec (reference range = 10–14)
APTT = 65 sec (reference range = 28–36)
 Transaminases = elevated (AST:ALT ratio greater than 1)
Total and direct bilirubin = elevated
These clinical presentations and laboratory results are consistent with:
A. Inherited factor VII deficiency
B. DIC
C. Cirrhosis of the liver
D. von Willebrand disease
Hemostasis/Correlate clinical and laboratory data/Coagulation disorders/3
7. When performing a mixing study, the patient’s APTT is corrected to 12% of normal.
What is the most appropriate interpretation of these findings?
A. The APTT is considered corrected
B. The APTT is considered uncorrected
C. The laboratory protocol should be followed for the interpretation of correction
D. A circulating anticoagulant can be ruled out
Hemostasis/Correlate clinical and laboratory data/Mixing studies/3

Answers to Questions 5–7

5. D Factor VIII inhibitor is found in 20% to 25% of patients with hemophilia receiving
replacement therapy. It may also develop in patients with immunologic problems,
women after childbirth, and patients with lymphoproliferative and plasma cell
disorders, or it may develop in response to medications. Factor VIII inhibitor is an IgG
with an inhibitory effect that is time and temperature dependent. The presence of factor
VIII inhibitor causes elevated APTT in the face of a normal PT. Mixing studies in
factors VIII and IX deficiencies will correct the prolonged APTT both at the immediate
mixing stage and after incubation for 2 hours. APTT would not be corrected by mixing
studies in the presence of factor VIII inhibitor. In addition, factor VIII inhibitor is
associated with bleeding. Lupus anticoagulant is associated with thrombosis and not
bleeding unless it coexists with thrombocytopenia, which is not the case in this patient.
6. C The clinical presentation and laboratory results in this patient are indicative of cirrhosis
of the liver. Most of the clotting factors are made in the liver. A decrease in multiple
clotting factors is associated with prolonged PT and APTT. Macrocytosis and target
cells are present in liver disease. The liver changes the unconjugated bilirubin to
conjugated bilirubin. Conjugated bilirubin is excreted into the intestines, where
bilirubin is converted to urobilinogen and excreted into feces. In cirrhosis of the liver,
both necrosis and obstruction caused by scarring produce increases in unconjugated
and conjugated bilirubin, respectively. In addition, the liver enzymes are elevated (the
AST:ALT ratio is less than 1 in necrotic liver diseases, such as hepatitis, but not in
cirrhosis).
7. C Interpretation of correction studies varies among different laboratories. Some define
correction when the mixing study result falls within 10% of the normal plasma; other
laboratories conclude correction when the mixing result falls within 5 seconds of
normal plasma, or a value within the APTT reference range. Only 50% factor activity
is required for normal PT or APTT. A circulating anticoagulant typically results in
failure to correct the APTT with normal plasma.
8. A standard blue-top tube filled appropriately (with 4.5 mL blood) was submitted to the
laboratory for preoperative PT and APTT testing. The results of both tests were
elevated. The patient’s PT and APTT from the previous day were within normal limits,
and he was not on heparin therapy. Which is the most appropriate first step to
investigate the abnormal results?
A. Report the result as obtained
B. Perform a mixing study
C. Check the sample for a clot
D. Report APTT only
Hemostasis/Apply knowledge to identify sources of errors/Specimens/3
9. A plasma sample submitted to the laboratory for PT testing has been stored for 25 hours
at 4°C. PT is shortened. What is the most probable cause?
A. Factor VII deficiency
B. Activation of factor VII caused by exposure to cold temperature
C. Lupus inhibitor
D. Factor X inhibitor
Hemostasis/Apply knowledge to identify sources of errors/Specimen storage/3
10. APTT is not increased in a patient receiving heparin. Which of the following factors
may be associated with the lack of response to heparin therapy in this patient?
A. Protein C deficiency
B. AT deficiency
C. Protein S deficiency
D. Factor VIII deficiency
Hemostasis/Correlate clinical and laboratory data/Inhibitors/3
11. A 50-year-old patient was admitted to the emergency department with a complaint of
pain in the right leg. The leg was red, swollen, and warm to the touch. DVT was
suspected, and the patient was started on heparin therapy. Which of the following is
(are) the proper protocol(s) to evaluate patients receiving heparin therapy?
A. Baseline APTT and PLT count; APTT testing every 4 to 6 hours after the initial heparin
bolus
B. Repeat APTT 5 days after heparin therapy to adjust the therapeutic dose
C. Monitor the PLT count daily and every other day after heparin therapy is completed
D. Monitor PT daily to adjust the therapeutic dose
Hemostasis/Correlate clinical and laboratory data/Heparin therapy/2

Answers to Questions 8–11

8. C A clot can form because of inadequate mixing of the sample after venipuncture, if the
blood fills the evacuated tube at a slow rate, or with traumatic venipuncture. In vitro,
blood clots result in consumption of the clotting factors and, therefore, prolongation of
PT, APTT, and other clot-based assays. If the clotting factors have been activated but
the clot formation is incomplete, it may result in shortening of PT and APTT.
Checking the sample for a clot is the most reasonable step in this case.
9. B Samples for evaluation of PT are stable for 24 hours if kept at room temperature.
Prolonged exposure to cold will activate factor VII, resulting in decreased PT.
 10. B AT deficiency in patients receiving heparin therapy may lead to heparin resistance
and, therefore, lack of prolongation of APTT. AT is a heparin cofactor and, as such,
increases heparin activity by 1,000-fold. Deficiency of AT is associated with poor
response to heparin therapy.
11. A Baseline PLT count and APTT should be performed on all patients prior to
administration of heparin. APTT should be repeated every 4 to 6 hours after bolus
injection (high dose). Response to heparin therapy varies among patients for the
following reasons: heparin half-life is decreased in extended thrombosis, and the
anticoagulant activities of heparin change based on nonspecific binding of heparin to
plasma proteins. Therefore, heparin therapy should be closely monitored. Heparin
dosage can be adjusted based on the anti–factor Xa assay. In addition, the PLT count
should be monitored regularly during heparin therapy because decrease of the PLT
count to 50% below the baseline value is significant and may be associated with HIT.
PT is not used to monitor heparin therapy.

12. Patient History:

A 46-year-old female was admitted to the emergency department with complaints of
headache, dizziness, lethargy, nausea, vomiting, and weakness. The patient had
undergone a gastrectomy procedure 4 months earlier for removal of adenocarcinoma of
the stomach and had been placed on mitomycin therapy. Diagnostic procedures
indicated recurrence of the carcinoma.
Admission Complete Blood Count (CBC) Results
Patient Reference Range
WBCs 17.1 × 109/L 4.8–10.8 × 109/L
RBCs 2.29 × 1012/L 3.80–5.50 × 1012/L
Hgb 8.1 g/dL 12.0–15.2 g/dL
Hct 23% 37%–46%
MCV 95.7 fL 79–101 fL
MCH 35.4 pg 27–33 pg
MCHC 35.0 % 31%–34 %
RDW 18.5 11.5–14.5
PLTs 48.0 × 109/L 140–450 × 109/L
MPV 11.2 7.4–9.4
DIFERENTIAL COUNTS (%)
Segmented neutrophils 79 30%–70%
Band neutrophils 3 0%–10%
Lymphocytes 11 20%–50%
Monocytes 6 2%–12%
 Basophils 1 0%–2%
NRBCs (/100 WBCs) 3 0
Manual platelet count 18 × 109/L 140–450 × 109/L
Marked anisocytosis None
Marked RBC None
fragmentation
PT, APTT, and TT Normal
ADDITIONAL LABORATORY DATA
Urinalysis PATIENT REFERENCE
RANGE
pH 5.0 5–7
Protein 30.0 mg/dL 0–15 mg/dL
RBCs 60–100/μ.
Casts 10/high-power field (hpf) Not detectable
granular/hyaline
Plasma PATIENT REFERENCE
RANGE
Creatinine 3.1 mg/dL 0.7–1.3 mg/dL
BUN 39 mg/dL 8–22 mg/dL
Haptoglobin 5.0 mg/dL 50–150 mg/dL
These clinical manifestations and laboratory results are consistent with:
A. ITP
B. von Willebrand disease
C. TTP
D. DIC
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/3

Answer to Question 12
12. C The clinical manifestations and laboratory results in this patient are consistent with
TTP. The clinical manifestations of TTP include MAHA, thrombocytopenia, fever,
renal failure, and neurological symptoms. The neurological symptoms in this patient
are manifested by headache, dizziness, nausea, and vomiting. Weakness and lethargy
are signs and symptoms of anemia. Low Hgb and Hct with normal MCV and MCHC
indicate a normocytic normochromic anemia. The presence of schistocytes in
peripheral blood, with low platelet counts and low haptoglobin, are consistent with
MAHA. The high BUN and creatinine levels are characteristic of renal failure. The
platelet count, performed on admission, was done on a hematology analyzer and was
 falsely elevated because of the presence of microcytes or fragmented RBCs. The
manual platelet count was much lower. The coagulation tests are normal in TTP. In
von Willebrand disease, the platelet count is normal and the APTT is usually
abnormal. ITP is characterized by thrombocytopenia but not hemolytic anemia (HA).
DIC is associated with a low platelet count, HA, and abnormal coagulation studies.
The acute onset of symptoms in this patient may be related to mitomycin used for the
treatment of gastric carcinoma in this patient.

13. Patient History

A 1-year-old infant was admitted with recurrent epistaxis for the past 5 days. Past
medical history revealed easy bruising and a severe nosebleed that had occurred when
he was 3 months of age, necessitating transfusion therapy. The mother had a severe
nosebleed 8 years ago. The father was reported to bleed easily after lacerations. The
patient was transfused with 2 units of packed RBCs on admission.
Admission Laboratory Results
Patient Reference Range
Hgb 4.5 g/dL 13–15 g/dL
Platelet count 249 × 109/L 150–450 × 109/L
PT 11.2 sec 11–13 sec
APTT 34 sec 28–37 sec
ADDITIONAL LABORATORY TESTS
Factor VIII assay 70% 50%–150%
PLT aggregation: Abnormal to ADP, EPI, and thrombin; normal to ristocetin
These clinical manifestations and laboratory results are consistent with which
condition?
A. von Willebrand disease
B. Bernard-Soulier syndrome
C. Glanzmann thrombasthenia
D. Factor VIII deficiency
Hemostasis/Correlate clinical and laboratory data/Platelet disorders/3

Answer to Question 13
13. C These clinical manifestations and laboratory results are consistent with Glanzmann
thrombasthenia. Epistaxis and easy bruising are characteristics of platelet disorders.
The positive family history is indicative of an inherited bleeding disorder. Laboratory
tests reveal a low Hgb level caused by epistaxis. The normal platelet count rules out
any quantitative platelet disorder. The platelet count is typically low in Bernard–
Soulier syndrome. Normal PT and APTT, combined with a normal factor VIII assay,
rule out coagulation disorders. The laboratory tests that confirm an inherited platelet
disorder are PLT aggregation studies. PLT aggregation is normal to ristocetin and
 abnormal to ADP, EPI, and thrombin. These results are consistent with Glanzmann
thrombasthenia. PLT aggregation is abnormal to ristocetin in von Willebrand disease
and Bernard–Soulier syndrome.

14. Patient History:

A 30-year-old female was referred to the hospital for evaluation for multiple
spontaneous abortions and current complaint of pain and swelling in her right leg. Her
family history is unremarkable.
Laboratory Tests Patient Reference Range
PT 14.5 sec 11–13 sec
APTT 63.0 sec 28–37 sec
TT 12.0 sec 10–15 sec
Mixing Study APTT
Preincubation and after 2-hour incubation at 37°C 57.0 sec
Platelet neutralization procedure
Patient plasma + freeze-thawed platelets APTT = 35 sec
Patient plasma + saline APTT = 59 sec
Anticardiolipin antibodies done by ELISA Negative
These clinical manifestations and laboratory results are consistent with:
A. Factor VIII inhibitor
B. Factor VIII deficiency
C. Anticardiolipin antibodies
D. Lupus anticoagulant
Hemostasis/Correlate clinical and laboratory data/Inhibitors/3
15. A 60-year-old patient was admitted to a hospital for a liver biopsy. The biopsy was
scheduled for 11:00 a.m. The coagulation results obtained at the time of admission
revealed prolonged PT with an INR of 4.5. What is the physician’s most appropriate
course of action?
A. Proceed with biopsy because prolonged PT is expected in liver disease
B. Postpone the procedure for a couple of days
C. Cancel the procedure and start the patient on vitamin K therapy
D. Put patient on vitamin K therapy and proceed with the procedure immediately
Hemostasis/Correlate clinical and laboratory data/INR/3

Answers to Questions 14–15

14. D These clinical manifestations and laboratory results are consistent with lupus
anticoagulant. Pain and swelling in the patient’s right leg may be indicative of
thrombosis. As many as 48% of women with repeated spontaneous abortions have
lupus anticoagulant or/and antibody to phospholipid, such as anticardiolipin antibodies.
 The unremarkable family history in this patient rules out an inherited thrombotic
disorder. Normal TT rules out fibrinogen disorders. Prolonged PT and APTT in the
absence of bleeding history eliminate the diagnosis of factor deficiency. The APTT test
performed on a mixture of patient plasma and normal plasma did not correct the
prolonged APTT. This result is indicative of an inhibitor. However, because the patient
is not bleeding, factor VIII inhibitor is not indicated. A negative anticardiolipin
antibody result rules out the possibility of anticardiolipin antibodies being responsible
for the patient’s clinical symptoms. The laboratory test result that confirms the
presence of a lupus anticoagulant is prolonged APTT that is not corrected when mixed
with normal plasma and that is neutralized by preincubation with platelet phospholipid
(an excess of platelet phospholipid neutralizes the antibody, resulting in normal
APTT).
15. C Performing liver biopsy in a patient with a prolonged PT and a high INR could have
life-threatening consequences. In this patient, the prolonged PT is likely caused by
liver disease. Vitamin K is stored in the liver and is essential for activation of factors
II, VII, IX, and X. Vitamin K needs bile (secreted by the liver) for its absorption. In
liver disease characterized by obstruction, bile is not secreted into the gastrointestinal
tract, and therefore, vitamin K is poorly absorbed. The most logical course of action is
the following: Start the patient on vitamin K therapy, repeat the PT test 4 days after
starting vitamin K administration, and cancel the biopsy until the patient’s PT returns
to normal.

16. A fresh blood sample was sent to the laboratory at 8:00 a.m. for the PT test. At 4:00
p.m., the doctor requested for the APTT test to be done on the same sample. What
should the technologist do?
A. Rerun the APTT on the 8:00 a.m. sample and report the result
B. Request a new sample for APTT
C. Run the APTT in duplicate and report the average
D. Mix patient plasma with normal plasma and run the APTT
Hemostasis/Select methods/Reagents/Specimen collection and handling/Specimens/3
17. An APTT test is performed on a patient and the result is 50 sec (reference range 27–37
sec). The instrument flags the result because of failure of the delta check. The patient
had had an APTT of 35 sec the previous day. The technologist calls the nursing unit to
check whether the patient is on heparin therapy. The patient is not receiving heparin.
What is the next appropriate step?
A. Check the patient’s family history for inherited factor VIII deficiency
B. Check to see if the patient has received any other anticoagulant medications
C. Perform mixing studies
D. Perform a factor VIII assay
Hemostasis/Select course of action/3
18. A patient was put on heparin therapy postoperatively for prevention of thrombosis. The
patient had the following laboratory results on admission: Platelet count = 350 × 109/L;
PT = 12 sec (reference: 10–13 sec); APTT = 35 sec (reference: 28–37). After 6 days of
heparin therapy, the patient complained of pain and swelling in her left leg. Her platelet
count dropped to 85 × 109/L, and her APTT result was 36 sec. The physician suspected
HIT and ordered the PLT aggregation test to be performed immediately. The heparin-
 induced PLT aggregation test result was negative. Heparin therapy was continued.
Several days later, the patient developed a massive clot in her left leg that necessitated
amputation. Which of the following should have been recognized or initiated?
A. The patient should have been placed on LMWH
B. The heparin dose should have been increased
C. The negative PLT aggregation does not rule out HIT
D. The patient should have been placed on warfarin therapy
Hemostasis/Correlate clinical and laboratory data/HIT/3

Answers to Questions 16–18

16. B According to the CLSI guidelines, samples for APTT should be centrifuged and tested
within 2 hours after collection. However, the sample is stable for 4 hours if stored at
4°C. APTT evaluates the clotting factors in the intrinsic and common coagulation
pathways, including factor VIII (intrinsic) and factor V (common). Factors VIII and V
are cofactors necessary for fibrin formation. However, they are both labile. Storage
beyond 4 hours causes falsely elevated APTT results. The medical laboratory scientist
should request a new sample for the APTT test.
17. B Traditional anticoagulant drugs, such as heparin and warfarin, are well known. Newer
anticoagulant drugs are available for the treatment and prevention of thrombosis. Some
of these new drugs have AT or anti–factor Xa effects and, therefore, increase PT,
APTT, and TT. Examples of these drugs are argatroban, which inhibits thrombin, and
fondaparinux, which inhibits factor Xa.
18. C Heparin therapy should be stopped immediately when clinical symptoms indicate
HIT. The blood sample should be tested at least 4 hours after heparin therapy is
discontinued. Early sampling for HIT testing may give a false-negative result because
of the neutralization of antibody by heparin. LMWH should not be used in patients
who develop HIT because LMWH can also cause HIT. Warfarin therapy can be started
in patients who respond to heparin therapy. Heparin therapy must overlap warfarin
therapy until the INR reaches a stable therapeutic range (2.0–3.0). Warfarin therapy
could not be used in this patient because of lack of response to heparin therapy. The
first step in the treatment of HIT is discontinuation of heparin, including intravenous
catheter flushes, heparin-coated indwelling catheters, UFH, and LMWH.

19. A 50-year-old female was admitted to a hospital for hip replacement surgery.
Preoperative tests were performed, and the results showed the following:
Hgb = 13.5 g/dL; Hct = 42%; PT = 12 sec; APTT = 36 sec.
The patient was bleeding during surgery, and postoperative test results revealed the following:
Hgb = 5.0 g/dL; Hct = 16%; PT = 8 sec; APTT = 25 sec.
What steps should be taken before releasing these results?
A. No follow-up steps are needed; report the results as obtained
B. Report Hgb and Hct results, adjust the anticoagulant volume, and redraw a new sample for
PT and APTT
C. Call the nurse and ask if the patient is receiving heparin
D. Because the patient is severely anemic, multiply the PT and APTT results by two and
 report the results
Hemostasis/Select course of action/3
20. A 45-year-old woman visited her doctor complaining of easy bruising and menorrhagia
occurring for the past few weeks. The patient had no history of excessive bleeding
during child birth several years earlier or during a tonsillectomy in childhood. Her
family history was unremarkable.
Laboratory Tests Patient Reference
Range
PT 45 sec 11–13 sec
APTT 125 sec 28–37 sec
TT 14 sec 10–15 sec
Mixing studies (patient plasma + normal PT = 40 sec; APTT = 90
plasma): sec
Platelet count and morphology: normal
Liver function tests: normal
These clinical manifestations and laboratory results are consistent with:
A. Factor VIII inhibitor
B. Factor V inhibitor
C. Factor VIII deficiency
D. Lupus anticoagulant
Hemostasis/Correlate clinical and laboratory data/Inhibitors/3

Answers to Questions 19–20

19. B The anticoagulant:blood ratio should be adjusted for the PT and APTT tests in
patients with a severe anemia. The standard anticoagulant volume (0.5 mL) is not
sufficient for the large quantity of plasma in these patients, causing unreliable PT and
APTT results. The low Hgb and Hct in this patient were caused by severe bleeding
during surgery. To get accurate PT and APTT results, the amount of anticoagulant is
adjusted according to the following formula: (0.00185)(V) (100–H) = C, where V =
blood volume in mL; H = patient’s Hct; and C = volume of anticoagulant in mL. A
new sample should be drawn to rerun the PT and APTT. There are other causes for
decreased PT and APTT, such as increased fibrinogen and increased factor VIII;
however, the preanalytical variables affecting unreliable results should be ruled out
first. Heparin therapy would increase PT and APTT.
20. B The absence of a positive family history in this patient indicates acquired
coagulopathy. Because both the PT and APTT test results are abnormal, the clotting
factor involved is most probably in the common pathway. The lack of correction by
mixing studies suggests the presence of an inhibitor. Factor V antibodies are the most
common antibodies among the clotting factors of the common pathway (I, II, V, and
X). Factor V antibodies are reported to be associated with surgery; some antibiotics,
 such as streptomycin; exposure to blood products or the bovine form of “fibrin glue.”
Patients with antibodies to factor V may require long-term therapy with
immunosuppressive drugs. Acute bleeding episodes may be treated by platelet
transfusions. The PT test is normal in patients with factor VIII deficiency and factor
VIII inhibitor. Lupus anticoagulant is not present with bleeding unless associated with
coexisting thrombocytopenia.

BIBLIOGRAPHY
1. Bick RL. Disorders of Thrombosis and Hemostasis. 3rd ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2002.
2. Marder VJ, Aird WC, Bennett JS, et al. Hemostasis and Thrombosis, Basic Principles and Clinical Practice. 6th ed.
Philadelphia, PA: Lippincott Williams and Wilkins; 2013.
3. Greer JP, Arber DA, Glader B, et al. Wintrobe’s Clinical Hematology. 13th ed. Philadelphia, PA: Lippincott Williams and
Wilkins; 2014.
4. Kaushansky K, Lichtman MA, Beutler E, et al. Williams Hematology. 8th ed. New York, NY: McGraw-Hill; 2010.
5. Nathan DG, Orkin SH, Ginsburg D, et al. Hematology of Infancy and Childhood. 7th ed. Vol. 2. Philadelphia, PA: W.B.
Saunders; 2008.
6. Keohane EM, Smith LJ, Walenga JM. Rodak’s Hematology, Clinical Principles and Applications, 5th ed. Philadelphia, PA:
Elsevier; 2016.