Technique of Blood Collection MODULE

Hematology and Blood

Bank Technique

2
Notes
TECHNIQUE OF BLOOD
COLLECTION

2.1 INTRODUCTION
Blood is collected from the vein for various hematological investigations. In
order to obtain accurate and precise results in the laboratory which will help the
clinician to make a correct diagnosis of the patient’s disease, it is of paramount
importance to collect the blood sample in a correct manner.
Each sample is sent to the laboratory accompanied by a laboratory requisition
form filled in by the clinician. Brief clinical details and any other relevant
information must be mentioned on the form.
Prior to blood sample collection it is essential to check the patient’s identity and
make sure that it corresponds to the name and other details mentioned on the
requisition form.
Blood can be withdrawn from the vein, usually the antecubital vein on the
forearm (Venous blood) or from the finger or heel (Capillary blood). Venous
blood is preferred. It can be collected using a syringe and needle or a vacuum
tube. Both these methods will be described seperately.

OBJECTIVES
After reading this lesson, you will be able to:
z describe the technique of collection of venous blood using a syringe and
needle and a vacuum tube
z describe the method of collection of capillary blood
z explain the various anticoagulants used in hematology laboratory and their
action.
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 MODULE Technique of Blood Collection

Hematology and Blood

Bank Technique
2.2 COLLECTION OF VENOUS BLOOD
Blood is usually withdrawn from the antecubital vein or any other vein which
is well identified on the forearm. The vein selected should be large, readily
accessible, and sufficiently close to the surface to be seen and palpated

Preparation of venipuncture site

Notes Clean the skin of the area around the identified vein with 70% isopropyl alcohol
in a circular fashion beginning at the site and moving outward. Allow to dry
spontaneously. Do not touch the venipuncture site after it has been cleaned.
Apply a tourniquet 3-4 inches above the venipuncture site. Ask the patient to
make a fist a few times. Veins suitable for puncture will then become more
apparent. Veins can become distended and easier to enter by allowing the arm
to hang down for 2 or 3 minutes or by gently slapping the site of puncture.

Fig. 2.1: Clean the area of the venipuncture site

using circular anticlockwise motion

Collection of venous blood using a syringe

1. Clean hands thoroughly with soap and water.
2. Write the name and hospital number of the patient on the tube in which
blood is to be collected. A printed label with these particulars can also be
used for patient identification.
3. Place the needle into the syringe. Keep the cap over the needle capped till
it is used. Check that the syringe works smoothly.
4. With the needle bevel up and parallel to the surface of the skin insert it
into the vein. Appearance of blood in the hub of the needle indicates that
the needle has successfully entered the vein. Release the tourniquet as soon
as blood enters the syringe.

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Technique of Blood Collection MODULE
5. Withdraw the piston slowly to avoid frothing. Hematology and Blood
Bank Technique
6. After obtaining the requisite amount of blood, place a sterile gauze pad over
the point where the needle entered the skin and deftly withdraw the needle
simultaneously while applying pressure over the site.
7. Deliver the blood gently into the specified receiver. Cap it firmly to prevent
leakage.
8. Maintain light pressure on the gauze pad over venipuncture site till the Notes
bleeding stops and then cover the puncture site with a small adhesive
dressing.
9. Destroy the needle in a special device (needle destroyer) immediately after
use. DONOT break, bend or recap needles after use.
10. Place the used swab, syringe and any other contaminated material in a
puncture resistant container for adequate disposal.

Collection of venous blood using a vacuum tube

The Vacutainer system consists of a double-pointed needle, a plastic holder or
adapter, and several vacuum tubes with rubber stoppers of various colors
depending on the sample to be collected. The color of the vacuum tube indicates
the anticoagulant which it contains. The blood is directly collected into the tube
from the vein.

Procedure
1. Place the identification details of the patient on each vacuum tube and
ensure that they tally with the form.
2. Identify the vein and clean the area as described before. Apply a tourniquet
3-4 inches above the identified vein. Do not touch the venipuncture site after
cleaning.
3. Place the vacuum tube in a reusable plastic holder and attach a disposable
needle to it. Insert the tube into the holder till the top of the stopper is level
with the marked guideline.
4. Place the patient’s arm in a downward position to reduce the risk of
backflow of any anticoagulant into the patient’s circulation.
5. Insert the needle into the vein. Push the tube into the needle, puncturing
the stopper/vacuum seal.
6. Remove the tourniquet as soon as the blood appears in the tube. Do not
allow contents of the tube to come into contact with the stopper
7. Do not allow the contents of the tube to come into contact with the stopper
during the procedure.

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 MODULE Technique of Blood Collection

Hematology and Blood 8. If more than one sample is required, successive tubes may be fitted into
Bank Technique
the holder after removing the previous tube and blood collected. The needle
remains in the vein. While each successive tube is filling, the previous tube
may be inverted gently to mix the sample well. Do not shake vigorously
as this may lead to hemolysis of the blood sample.
9. After completion of blood collection, remove the holder and cover the site
with a sterile swab and apply pressure till bleeding stops completely.
Notes
10. Destroy the needle in the destroyer without recapping it.

Fig. 2.2: Collection of venous blood using a vacuum tube

2.3 TYPES OF VACUUM TUBES

Vacuum tubes with different colored caps are available. Each contains a different
anticoagulant and is used for various hematological tests as described below.
Color of cap Anticoagulant Test
Purple EDTA complete blood counts
Red - for tests which need serum
Blue Sodium citrate coagulation tests
Grey fluoride blood sugar

2.4 COLLECTION OF CAPILLARY BLOOD

This can be obtained by skin puncture with a needle or lancet and is specially
used in small children or very obese adults in whom venepuncture fails. Samples
can be used for making peripheral blood films, performing hematocrit/Hb and
point of care testing.
In adults capillary blood sample can be obtained from the lateral side of tip of
the 3rd or 4th finger while in infants the sample can be obtained by a deep
puncture of the plantar surface of the heel.
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Technique of Blood Collection MODULE
Procedure Hematology and Blood
Bank Technique
1. Clean the area with 70% alcohol and allow it to dry spontaneously. Puncture
the skin to a depth of 2-3 mm with a sterile disposable lancet/needle.
2. Wipe the first drop of blood and squeeze gently to allow free flow of blood
and collect the sample. In an adequate puncture, large drops of blood should
exude spontaneously. Do not squeeze firmly as this gives unreliable results.
Notes

INTEXT QUESTIONS 2.1

Match the following
Test Colour of cap
1. Complete blood count (a) Grey
2. Coagulation test (b) Purple
3. Blood sugar (c) Red
4. Tests which need serum (d) Blue

2.5 ANTICOAGULANTS USED IN HEMATOLOGY

The anticoagulants used commonly in the hematology laboratory are
EDTA: Ethylene Diamine Tetra Acetic acid
Sodium citrate
Heparin
EDTA: This is used for complete blood counts. The sodium and potassium salts
can both be used but the dipotassium salt is preferred as it is more soluble. The
dilithium salt can also be used but like the disodium salt is less soluble. The
dipotassium salt is used in solid form. The International Council for
Standardization in Hematology recommends use of the dipotassium salt at a
concentration of 1.50±0.25mg/ml of blood. Coating the inside of a blood
collection vial with a thin layer of EDTA improves the speed of uptake by blood.
It exerts it’s action by removing calcium which is essential for coagulation.
If EDTA is used in excess, it causes shrinkage of red cells and leucocytes. A
significant decrease in hematocrit and increase in MCHC also occur. Platelets
swell and disintegrate causing a false high count. It is thus important to add the
correct amount of blood to the vial.

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 MODULE Technique of Blood Collection

Hematology and Blood Trisodium citrate: This is used in coagulation studies in a ratio of 9 volumes
Bank Technique
of blood to one volume of anticoagulant (32g/L) (0.5ml citrate+4.5ml blood).
It binds calcium thus preventing coagulation. It can also be used for estimation
of ESR by Westergren method in a ratio of 4 volumes of blood to 1 volume of
sodium citrate.
Heparin: The sodium or lithium salt of heparin is used at a concentration of 10-
20IU/ml of blood for osmotic fragility and for red cell enzyme studies like
Notes glucose-6-phosphate dehydrogenase. It does not change red cell size and is the
best anticoagulant for osmotic fragility. It can also be used for immunophenotyping.
Heparin is not suitable for complete blood counts as it induces platelet and
leucocyte clumping. It should also not be used for making peripheral smears as
it gives a faint blue background color after staining smears by Romanowsky
dyes.

Types of Samples Collected for Hematological Investigations

Whole blood: This is used for performing complete blood counts including
reticulocyte count and for making peripheral blood films.
Serum: If blood is allowed to clot at room temperature, a straw colored fluid
appears which is called serum. This may be admixed with red cells which can
be removed by centrifugation at 1200g for 10 minutes. It is used for various
biochemical tests and also serum protein electrophoresis to diagnose plasma cell
disorders such as multiple myeloma. Serum lacks coagulation factors.
Plasma: This is obtained by centrifugation of anticoagulated blood and is used
for coagulation studies.

INTEXT QUESTIONS 2.2

1. The anticoagulant used for complete blood counts is
(a) EDTA
(b) Heparin
(c) Sodium citrate
(d) Any of the above
2. For coagulation studies the ratio of blood to anticoagulant is
(a) 9 : 1
(b) 7 : 1
(c) 8 : 1
(d) Any of the above

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Technique of Blood Collection MODULE
3. Complete the sentence Hematology and Blood
Bank Technique
EDTA exerts it’s action as an anticoagulant by ...................

WHAT HAVE YOU LEARNT

z Blood is collected from the vein for various hematological investigations Notes
z Blood can be withdrawn from the vein, usually the antecubital vein on the
forearm or for capillary blood form the finger or heel
z Blood can be collected using a syringe and needle or a vacuum tube
z The vein should be large, readily accessible, and sufficiently close to the
surface of the skin to be seen and palpated
z Write the patient name and hospital number on the tube
z The skin area around the identified vein should be cleaned with 70%
isopropyl alcohol
z Apply a tourniquet 3-4 inches above the venipuncture site
z Insert the needle into the vein and withdrawn the required amount of blood
slowly
z Deliver the blood in the specific container
z Maintain even pressure on the venipuncture site till bleeding stops
z Destroy the needle used immediately
z Vacuum tubes with different coloured caps are available and each contains
different anticoagulant used for various hematological tests
z Capillary blood can be obtained from the lateral side of tip of 3rd or 4th
finger and for infants from plantar surface of heel
z The anticoagulants used commonly in the hematology laboratory are
Ethylene Diamine Tetra Acetic acid (EDTA), Sodium citrate, Heparin

TERMINAL QUESTIONS
1. Explain the different types of vacuum tubes
2. What the commonly used anticoagulants in hematology

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 MODULE Technique of Blood Collection

Hematology and Blood

Bank Technique
ANSWERS TO INTEXT QUESTIONS

2.1
1. (b)
2. (d)
Notes
3. (a)
4. (c)

2.2
1. (a)
2. (a)
3. Removing the calcium

16 HEMATOLOGY AND BLOOD BANK TECHNIQUE