Evaluation of Abnormal Liver

Tes ts
Tinsay A. Woreta, MD, Saleh A. Alqahtani, MD*

KEYWORDS

Aminotransferases
Alkaline phosphatase
Hepatocellular injury
Cholestasis

Bilirubin metabolism

KEY POINTS

Serum aminotransferases are sensitive markers of hepatocellular injury.

Assessing the pattern and degree of elevation in aminotransferases can help suggest the
cause of liver injury.

Elevation in serum alkaline phosphatase occurs as a result of cholestasis, which may
result from intrahepatic causes, extrahepatic obstruction, or infiltrative disorders of the
liver.

Hyperbilirubinemia may occur as the result of both hepatocellular and cholestatic injury.

Albumin and prothrombin time are true markers of liver synthetic function.

INTRODUCTION

The use of serum biochemical tests plays an important role in the diagnosis and man-
agement of liver diseases. The routine use of such tests has led to the increased
detection of liver diseases in otherwise asymptomatic patients, often providing the
first clue of the presence of liver pathology. Such laboratory tests, in addition to a care-
ful history, physical examination, and imaging tests, can help clinicians determine the
cause of liver disease in most cases.
The term “liver function tests” is commonly used to refer to a combination of liver
biochemical tests, including serum aminotransferases, alkaline phosphatase (AP),
and bilirubin. This is a misnomer, because aminotransferases and AP are markers
of hepatocyte injury and do not reflect liver synthetic function. Traditionally, liver injury
has been characterized as primarily hepatocellular versus cholestatic based on the
degree of elevation of aminotransferases compared with AP (Table 1). Although
such a distinction can help direct initial evaluation, there is often significant overlap
in the presentation of various liver diseases, which often have a mixed pattern.1 It is

Division of Gastroenterology and Hepatology, The Johns Hopkins Hospital, 1830 East Monu-
ment Street, Suite 428, Baltimore, MD 21287, USA
* Corresponding author.
E-mail address: salqaht1@jhmi.edu

Med Clin N Am 98 (2014) 1–16

http://dx.doi.org/10.1016/j.mcna.2013.09.005 medical.theclinics.com
0025-7125/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved.
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
2 Woreta & Alqahtani

Table 1
Categorization of liver diseases by pattern of elevation of liver enzymes

Liver Disease Category Aminotransferases Alkaline Phosphatase

Hepatocellular [[ [
Cholestatic [ [[

useful to classify liver biochemical tests into the following categories2: (1) markers of
hepatocellular injury (aminotransferases and AP); (2) tests of liver metabolism (total
bilirubin); (3) tests of liver synthetic function (serum albumin and prothrombin time
[PT]); and (4) tests for fibrosis in the liver (hyaluronate, type IV collagen, procollagen
III, laminin, FibroTest [BioPredictive, Paris, France], and FibroScan [Echosens, Paris,
France]).
Furthermore, when evaluating patients with abnormal liver enzyme or function tests,
it is helpful to define the liver injury as acute versus chronic. Liver disease is considered
chronic if the abnormalities in liver enzyme tests or function persist for more than
6 months.

MARKERS OF HEPATOCELLULAR INJURY

The liver contains a multitude of enzymes in high concentration, some of which are
present in the serum in very low concentrations. Injury to the hepatocyte membrane
leads to leakage of these enzymes into the serum, which results in increased serum
concentrations within a few hours after liver injury. Serum enzymes tests can be cate-
gorized into two groups2: enzymes whose elevation reflects generalized damage to
hepatocytes (aminotransferases); and enzymes whose elevation primarily reflects
cholestasis (AP, g-glutamyltransferase [GGT], 50 nucleotidase [50 -NT]).
Aminotransferases
The aminotransferases (previously called transaminases) are located in hepatocytes
and are sensitive indicators of hepatocyte injury. They are useful in detecting acute he-
patocellular diseases, such as hepatitis.2 They consist of aspartate aminotransferase
(AST) and alanine aminotransferase (ALT). Aminotransferases catalyze the transfer of
the a-amino groups from aspartate or alanine to the a-keto group of ketoglutaric acid,
forming oxaloacetic acid and pyruvic acid, respectively. The enzymatic reduction of
oxaloacetic acid and pyruvic acid to malate and lactate, respectively, is coupled to
the oxidation of the reduced form of nicotinamide dinucleotide to nicotinamide dinu-
cleotide. Because only nicotinamide dinucleotide absorbs light at 340 nm, this reac-
tion can be followed spectrophotometrically by the loss of absorptivity at 340 nm,
and provides an accurate method to assay aminotransferase activity.3
AST and ALT are present in the serum at low concentrations, usually less than 30 to
40 IU/L.4 The normal range varies among clinical laboratories, based on measure-
ments in specific populations. Several factors have been shown to influence ALT
activity, such as gender and obesity.5 Men tend to have a higher serum ALT activity
compared with women.
ALT is found in highest concentration in hepatocytes and in very low concentrations
in any other tissues. In contrast, AST is found in many other tissues including muscle
(cardiac, skeletal, and smooth muscle); kidney; and brain.2 Thus, ALT is a more
specific marker for liver injury. A ratio of AST/ALT greater than five, especially if ALT
is normal or slightly elevated, is suggestive of injury to extrahepatic tissues, such as
skeletal muscle in the case of rhabdomyolysis or strenuous exercise.
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
 Evaluation of Abnormal Liver Test 3

AST is present in the cytoplasm and mitochondria, whereas ALT is only present in
the cytoplasm (Fig. 1). About 80% of AST activity in the liver is derived from the mito-
chondrial isoenzyme, whereas most serum AST activity is derived from the cytosolic
isoenzyme in healthy persons.2 Processes leading to necrosis of hepatocytes or
damage to the hepatocyte cell membrane with increased permeability result in release
of AST and ALT into the blood.6
Assessing the pattern and degree of elevation in liver enzymes can help elucidate
the cause of liver injury and direct subsequent diagnostic testing and management.
Any type of liver cell injury can cause moderate elevations in serum aminotransferase
levels. Levels up to 300 IU/L are nonspecific and can be seen in any type of liver
disorder.7 Massive elevations with aminotransferase levels greater than 1000 IU/L
are almost exclusively seen in disorders associated with extensive hepatocellular
injury, most commonly caused by (1) toxin- or drug-induced liver injury, (2) acute
ischemic liver injury, or (3) acute viral hepatitis. Severe autoimmune hepatitis or Wilson
disease may also cause markedly elevated aminotransferases.
ALT is present in highest concentration in periportal hepatocytes (Zone 1) and in
lowest concentration in hepatocytes surrounding the central vein (Zone 3). AST, how-
ever, is present in hepatocytes at more constant levels (Fig. 2). Hepatocytes around
the central vein have the lowest oxygen concentration and thus are more prone to
damage in the setting of acute hepatic ischemia that can occur as the result of acute
hypotension or severe cardiac disease. The ensuing centrilobular necrosis results in a
rapid rise in aminotransferases, with AST value greater than ALT in the initial days of
hepatic injury.
After there is no further injury to hepatocytes, the rate of decline of AST and ALT
depends on their rate of clearance from the circulation. AST and ALT are catabolized
by the liver, primarily by cells in the reticuloendothethlial system. The plasma half-life
of AST and ALT are 17  5 hours and 47  10 hours, respectively.2 Thus, AST declines
more rapidly than ALT, and ALT may be higher than AST in the recovery phase of
injury.
Biliary obstruction, such as that caused by a common bile duct stone causing an
acute increase in intrabiliary pressure, may also lead to an acute, transient elevation
in aminotransferases.

Fig. 1. Location of AST and ALT in hepatocyte. ALT is only present in the cytoplasm, whereas
AST is present in both the cytoplasm and mitochondria. Eighty percent of AST activity in the
liver is derived from the mitochondrial isoenzyme.
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
4 Woreta & Alqahtani

Fig. 2. Concentration of AST and ALT according to location of hepatocytes in portal triad.

A wide variety of disorders can cause chronic elevation in serum transaminases.

Nonhepatic causes include thyroid diseases, celiac sprue, anorexia nervosa, Addison
disease, and muscle diseases.3 The most common hepatic causes of chronically
elevated liver enzymes are chronic viral hepatitis (hepatitis C and B); alcoholic liver dis-
ease; nonalcoholic fatty liver disease; and drugs. Drugs that can cause elevated
aminotransferase levels include antituberculosis drugs, such as isoniazid; antifungals,
such as azole drugs; and antiepileptic drugs. Other causes of chronic hepatitis include
(1) autoimmune hepatitis, which is most commonly seen in women and is associated
with other autoimmune diseases; (2) inherited metabolic liver disease, such as hered-
itary hemochromatosis, Wilson disease, and a1-antitrypsin deficiency; and (3) infiltra-
tive disorders, such as granulomatous liver diseases.
Aminotransferases levels are typically less than 400 IU/L in alcoholic liver disease.
An AST/ALT ratio of greater than two suggests alcoholic liver disease, whereas a ratio
greater than three is strongly suggestive.8 Low AST activity is secondary to a defi-
ciency of pyridoxal 50 -phosphate, which is common in alcoholics.9 Furthermore,
alcohol primarily damages mitochondria, which results in the release of AST into
the serum. Elevation in aminotransferase levels to greater than 1000 IU/mL is almost
never caused by alcoholic liver disease alone and suggests the presence of a
concomitant process, such as drug-induced liver injury or viral hepatitis. Chronic
alcoholic use leads to induction of the hepatic cytochrome CYP2E1, which converts
acetaminophen to the highly toxic intermediate, N-acetyl-p-benzoquinoneimine.
Thus, patients who drink alcohol on a chronic basis are at increased risk of developing
acetaminophen hepatotoxicity when consuming acetaminophen, even at doses less
than 4 g/day.
Although ALT is more elevated than AST in most forms of chronic liver disease with
the exception of alcoholic liver disease, the ratio of AST to ALT changes as fibrosis
develops. As fibrosis progresses, the AST/ALT ratio increases and becomes greater
than one after cirrhosis has developed in most cases. The platelet count also
decreases with advancing fibrosis and cirrhosis, because of the reduction of thrombo-
poetin synthesis by the liver and splenic sequestration of platelets in the setting of
portal hypertension. A platelet count of less than 150,000/mL in the absence of an un-
derlying hematologic disorder is highly suggestive of cirrhosis. Thrombocytopenia
may also be seen in acute alcoholic hepatitis because of bone marrow suppression
from alcohol toxicity.
Tables 2 and 3 summarize the causes of acute and chronic elevations in amino-
transferase levels, their pattern of AST and ALT elevation, and additional diagnostic
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
 Evaluation of Abnormal Liver Test 5

Table 2
Hepatic causes of acute elevation in aminotransferase levels and their patterns of liver
enzyme injury

Aminotransferase
Disease Levels Diagnostic Tests Clinical Clues
Drug- or toxin-induced liver injury
Acetaminophen Often >500 IU/L Acetaminophen level History of ingestion
Amanita phalloides AST > ALT — Wild mushroom
poisoning ingestion
Acute viral hepatitis
HAV Often >500 IU/L Anti-HAV IgM Risk factors
HBV ALT > AST HBsAg, HBV DNA,
anti-HBc
HCV (rare) — HCV RNA, anti-HCV
HDV (in setting of — Anti-HDV
HBV coinfection)
HEV — HEV IgM
HSV — HSV IgM
EBV — EBV IgM, EBV DNA
CMV — CMV IgM, CMV DNA
VZV — VZV IgM
Parvovirus B19 — Parvovirus B19 IgM
Ischemic hepatitis Often >500 IU/L — Recent hypotension
AST > ALT
Alcoholic hepatitis <400 IU/L — History of excess
alcohol
consumption
AST: ALT >2 Disproportionate
elevation in total
bilirubin
Acute biliary May be up to 1000 IU/L Imaging (eg, Acute onset of right
obstruction ultrasound) upper quadrant
pain
ALT > AST — History of
cholelithiasis

Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; CMV, cytomegalo-

virus; EBV, Epstein-Barr virus; HAV, hepatitis A; HBsAg, hepatitis B surface antigen; HBV, hepatitis B
virus; HCV, hepatitis C virus; HDV, hepatitis D virus; HEV, hepatitis E virus; HSV, herpes simplex virus;
VZV, varicella zoster virus.

testing indicated. An algorithm for the work-up of patients who present with a hepa-
tocellular pattern of liver injury is outlined in Fig. 3.

Cholestasis
Cholestasis refers to the pathologic condition in which there is impairment in the liver’s
ability to secrete bile. Disorders that predominantly affect the biliary system are
referred to as cholestatic diseases. They may affect the intrahepatic or extrahepatic
bile ducts, or both. In such disorders, the elevation in AP is the predominant feature.

Alkaline phosphatase
AP refers to a group of zinc metalloenzymes that catalyze the hydrolysis of several
organic phosphate esters at a neutral pH.3 APs are found in the canalicular membrane
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
6 Woreta & Alqahtani

Table 3
Hepatic causes of chronic elevation in aminotransferase levels and their patterns of liver
enzyme injury

Aminotransferase
Disease Levels Diagnostic Tests Clinical Clues
Chronic viral hepatitis
HCV <500 IU/L Anti-HCV, HCV RNA Risk factors
HBV ALT > ALT HBsAg, HBV DNA
HDV (in setting of — Anti-HDV
HBV coinfection)
Alcoholic liver disease <400 IU/L — History of excess
AST: ALT >2 alcohol consumption
Nonalcoholic fatty <300 IU/L — History of obesity,
liver disease ALT > AST diabetes,
hyperlipidemia
Drug-induced liver Up to 2000 IU/mL Improvement after Inciting medication
injury ALT > AST drug discontinuation
Autoimmune Up to 2000 IU/L ANA, antismooth Usually women, 30–50 y
hepatitis muscle antibody of age
ALT > AST IgG levels Presence of other
autoimmune diseases
Hereditary <200 IU/L Ferritin, iron saturation, Family history
hemochromatosis ALT > AST HFE gene testing
Wilson disease Up to 2000 IU/L Serum ceruloplasmin Age <40 y
ALT > AST 24 h urinary copper Low serum AP
collection
Slit-lamp examination —
a1-antitrypsin <100 IU/L Serum a1-antitrypsin Family history
deficiency level Presence of lung
disease at young age
Infiltrative liver <500 IU/L Imaging —
disease ALT > AST Liver biopsy
Cirrhosis of any cause <300 IU/L — Platelet count
<150,000/mL
AST > ALT Signs of portal
hypertension

Abbreviations: ALT, alanine aminotransferase; AP, alkaline phosphatase; AST, aspartate amino-
transferase; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; HCV, hepatitis C virus;
HDV, hepatitis D virus; HFE.

of hepatocytes, the membrane of bone osteoblasts, the brush border of small intesti-
nal mucosal cells, the proximal convoluted tubules of the kidney, the placenta, and
white blood cells.2 Most AP in the serum is derived from the liver, bone, and intestine.
Individuals with blood type O and B have been shown to have an elevation in serum AP
after consumption of a fatty meal.10 The level of serum AP also varies by age. Individ-
uals older than the age of 60 were found to have higher serum AP levels compared
with younger adults.11 Woman in the third trimester of pregnancy can have elevated
serum AP levels because of influx from the placenta.
The first step in the evaluation of an elevated serum AP level in asymptomatic pa-
tients is to determine the origin of the elevation. The most widely available and
accepted approach is to measure the activity of serum GGT or 50 -NT, liver enzymes
that are released in parallel to liver AP.7 The most precise method to determine the
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
 Evaluation of Abnormal Liver Test 7

Fig. 3. Algorithm for evaluation of patients with hepatocellular pattern of liver injury. ANA,
antinuclear antibodies; HAV, hepatitis A virus; HBsAG, hepatitis B surface antigen; HBV, hep-
atitis B virus; HCV, hepatitis C virus.

source of AP is to fractionate AP isoenzymes by electrophoresis; however, this is not

widely available in most laboratories.
Elevation in serum AP occurs when the hepatocyte canalicular membrane is disrup-
ted, causing translocation from the canalicular membrane to the basolateral (ie, sinu-
soidal) surface of the hepatocyte and leakage into serum. The mechanism of the
increase in AP is thought to be caused by the enhanced translation of messenger
RNA (mRNA) of AP in hepatocytes, rather than the failure to excrete AP.2 This seems
to be mediated by the action of bile acids, which induce synthesis of the enzyme and
may cause leakage into serum. Hence, in the setting of acute obstruction of the biliary
tree caused by gallstones, serum AP may initially be normal as de novo synthesis is
required, whereas marked elevation in aminotransferases may be seen.
Hepatocellular disease can lead to an increase in serum AP, which is generally less
than three times the upper limit of normal. Thus, moderate elevations in AP are
nonspecific and can be seen in viral hepatitis, chronic hepatitis, cirrhosis, congestive
heart failure, and infiltrative diseases of the liver.
The pattern of liver injury can be characterized based on the ratio (R) of the serum
ALT to AP (both expressed as multiples of the upper limit of normal): an R ratio of less
than two indicating cholestatic, greater than five hepatocellular, and two to five as
mixed cholestatic-hepatocellular injury.
The most common causes of cholestasis are listed in Table 4. Intrahepatic chole-
stasis is most commonly caused by medications, including certain antibiotics, antiep-
ileptic drugs, and anabolic steroids. It can also be caused by sepsis or total parenteral
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
8 Woreta & Alqahtani

Table 4
Common causes of intrahepatic and extrahepatic cholestasis

Disease Diagnostic Tests Clinical Clues

Intrahepatic causes
Primary biliary Antimitochondrial antibody Usually middle-aged women
cirrhosis Presentation with fatigue or
pruritus
Primary sclerosing MRCP or ERCP Presence of ulcerative colitis
cholangitis
Infiltrative disorders Imaging History of tuberculosis,
sarcoidosis, amyloidosis, or
malignancy
Liver biopsy Presentation with weight loss
Medication-induced Improvement after medication Inciting medication
injury discontinuation
Sepsis — History of recent/current
infection
TPN — TPN use
Extrahepatic causes
Choledocholithiasis Ultrasound History of biliary colic
ERCP or MRCP Acute onset of right upper
quadrant pain, fever, or
jaundice
Primary sclerosing ERCP Presence of ulcerative colitis
cholangitis
Malignancy
Pancreatic cancer Imaging (computed tomography Presentation with jaundice and
Cholangiocarcinoma or magnetic resonance weight loss
imaging)

Abbreviations: ERCP, endoscopic retrograde cholangiopancreatography; MRCP, magnetic reso-

nance cholangiopancreatography; TNP, total parenteral nutrition.

nutrition. Several diseases cause injury to the small intrahepatic bile ducts, including
primary biliary cirrhosis, primary or secondary sclerosing cholangitis, and infiltrative
disorders. Infiltrative disorders of the liver, such as sarcoidosis, tuberculosis, lym-
phoma, amyloidosis, and metastatic disease to the liver are commonly associated
with elevated alkaline phosphatase. Other causes are chronic liver allograft rejection
(which leads to ductopenia) and infectious hepatobiliary disorders in patients with
AIDS, such as cytomegalovirus or cryptosporidial infection (AIDS cholangioathy).
Causes of extrahepatic obstruction include benign and malignant conditions.
Benign causes include choledocholithiasis and primary or secondary cholangitis,
which may affect both the intrahepatic and extrahepatic biliary tree. Malignant causes
include cholangiocarcinoma, pancreatic, and ampullary cancers.
Imaging of the liver with ultrasonography is indicated in the initial assessment of pa-
tients with a predominantly cholestatic pattern of liver enzyme injury to assess for the
presence of biliary ductal dilatation. Dilated bile ducts suggest the presence of biliary
obstruction and warrants further evaluation with additional imaging (magnetic reso-
nance imaging, magnetic resonance cholangiopancreatography) or endoscopic retro-
grade cholangiopancreatography for diagnostic and possible therapeutic purposes.
Low levels of AP can present in patients with fulminant Wilson disease and is asso-
ciated with hemolytic anemia.
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
 Evaluation of Abnormal Liver Test 9

g-glutamyltransferase
GGT is an enzyme that catalyzes the transfer of the g-glutamyl group of peptides, such
as glutathione to other peptides or amino acids. GGT is present in the cell membranes
of many tissues including the proximal renal tubule, liver, pancreas, intestine, and
spleen.3 In the liver, GGT is located primarily on biliary epithelial cells and on the apical
membrane of hepatocytes. The predominant source of serum GGT is the liver. Entry of
GGT into the serum may occur by solubilization and release of membrane-bound GGT
or the death of biliary epithelial cells.12
Serum GGT is a sensitive indicator of the presence of injury to the bile ducts or liver.
However, its use is limited by its lack of specificity, because many nonhepatic dis-
orders can lead to elevation, including diabetes, hyperthyroidism, chronic obstructive
pulmonary disease, and renal failure.13 Alcohol abuse and certain medications, such
as barbiturates or phenytoin, lead to induction of hepatic microsomal GGT.14 The
main clinical use of GGT is to confirm the hepatic origin of elevated AP levels, because
GGT is not elevated in patients with bone disease.
50 nucleotidase
50 -NT catalyzes the hydrolysis of nucleotides, such as adenosine 50 -phosphate and
inosine 50 -phosphate, resulting in the release of free inorganic phosphate, which is
most commonly measured by assays of its activity. 50 -NT is found in the liver, intestine,
brain, heart, blood vessels, and pancreas.2 In the liver, it is found bound to the cana-
licular and sinusoidal membrane of hepatocytes. Its activity parallels that of AP, which
is likely a reflection of their similar location in the hepatocyte.15 Most studies show that
50 -NT and AP have equal clinical use in the detection of hepatobiliary disease.2 Like
GGT, its clinical value lies in its ability to determine the origin of elevated serum AP
levels, because its elevation in this setting strongly suggests a hepatic origin. The
algorithm for the evaluating patients with a predominant elevation in AP is summarized
in Fig. 4.

TESTS OF LIVER METABOLISM: TOTAL BILIRUBIN

Bilirubin is a naturally occurring pigment derived from the breakdown of heme-

containing proteins. Most of the 250 to 300 mg of bilirubin produced each day is
derived from the breakdown of hemoglobin in senescent red blood cells.16 The
remainder is derived from the premature destruction of erythroid cells in the bone
marrow and from the turnover of heme-containing proteins in tissues in the body.17
The liver has a high concentration of heme-containing proteins with high turnover
rates, such as the cytochrome P-450 enzymes.
The formation of bilirubin occurs primarily in reticuloendothelial cells in the liver and
spleen. The first step consists of the oxidation of heme by heme oxygenase to form
biliverdin. The second reaction is the reduction of biliverdin by biliverdin reductase
to form bilirubin. Unconjugated bilirubin is lipid-soluble and insoluble in water. Thus,
to be transported in blood, unconjugated bilirubin must be bound to albumin, which
occurs in a reversible, noncovalent fashion. Unconjugated bilirubin is thus not filtered
by the kidney because it is always bound to albumin in the serum. Bilirubin is then
transported to the liver, where it is taken up by hepatocytes by carrier-mediated
membrane transport. In the hepatocyte, it is bound to glutathione-S-transferases.
Bilirubin is then conjugated by a family of enzymes called uridine diphospho-
glucuronosyltransferase (UDP-glucuronosyltransferase). Conjugated bilirubin is
water-soluble and thus may be excreted by the kidney. Conjugated bilirubin is trans-
ported across the canalicular membrane into bile by active transport against a con-
centration using ATP. This is the rate-limiting step in bilirubin excretion.2
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
10 Woreta & Alqahtani

Fig. 4. Algorithm for evaluation of patients with elevated alkaline phosphatase. ERCP,
endoscopic retrograde cholangiopancreatography.

The terms direct and indirect bilirubin originated from the van den Bergh method of
measuring bilirubin concentration.18 In the assay, bilirubin reacts with diazotized
sulfanilic acid and divides into two dipyrrl azopigments that absorb light maximally
at 540 nm. The direct fraction reacts with diazotized sulfanilic acid in 1 minute in the
absence of alcohol, and provides an estimate of the concentration of conjugated
bilirubin in the serum. The total serum bilirubin concentration is then ascertained by
the addition of alcohol and determination of the amount that reacts in 30 minutes.
The indirect fraction is thus calculated as the difference between the total and direct
bilirubin concentrations. Normal total serum bilirubin concentration is less than
1 mg/dL using the van den Bergh method of bilirubin measurement. The direct fraction
comprises as much as 30% or 0.3 mg/dL of the total.
Newer techniques for the measurement of serum bilirubin use high-performance
liquid chromatography. These techniques have revealed that almost all of serum bili-
rubin in healthy persons is unconjugated. Furthermore, it seems that there is a fraction
of conjugated bilirubin that is covalently bound to albumin.19 This fraction increases in
patients with cholestasis and hepatobiliary disorders, when the excretion of conju-
gated bilirubin is impaired, resulting in increased serum concentration of conjugated
bilirubin. This explains the prolonged elevation in bilirubin seen in patients recovering
from hepatobiliary injury, because the clearance rate of bilirubin bound to albumin
from serum is determined by long half-life of albumin (about 21 days) and not the
shorter half-life of bilirubin (about 4 hours).19 This also explains why bilirubinuria is
not present in some patients with conjugated hyperbilirubinemia during the recovery
phase of their illness.
The concentration of bilirubin in the serum is determined by the balance between
bilirubin production and clearance by hepatocytes. Thus, elevated serum bilirubin
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
 Evaluation of Abnormal Liver Test 11

levels may be caused by (1) excessive bilirubin production, which occurs in states
of increased red blood cell turnover, such as hemolytic anemias or hematoma
resorption; (2) impaired uptake, conjugation, or excretion of bilirubin; and (3)
release of unconjugated or conjugated bilirubin from injured hepatocytes or bile
ducts.7
The presence of unconjugated hyperbilirubinemia (defined as direct bilirubin frac-
tion <20%) is rarely caused by liver disease. It is primarily seen in hemolytic disorders,
such as sickle cell disease or hereditary spherocytosis, or in setting of hematoma
resorption. In general, the total serum bilirubin is less than 5 mg/dL in such cases.
If hemolysis is ruled out, the most likely cause of mild elevation in indirect bilirubin
in an otherwise asymptomatic patient is Gilbert syndrome. This is the result of a ge-
netic defect leading to a mild decrease in the activity of UDP-glucuronosyltransferase.
Total bilirubin is usually in the range of 2 to 4 mg/dL. Levels increase during times of
fasting or stress. No further evaluation is indicated if Gilbert disease is suspected,
because there are no clinical sequelae. Crigler-Najjar syndrome type 1 is a rare,
autosomal-recessive disorder that results from near complete absence of UDP-
glucuronosyltransferase and leads to severe unconjugated hyperbilirubinemia and
kernicterus in newborns. Crigler-Najjar syndrome type 2 results from a milder form
of UDP-glucuronosyltransferase deficiency, and patients are generally asymptomatic.
Unlike unconjugated hyperbilirubinemia, the presence of conjugated hyperbilirubi-
nemia (and hence hyperbilirubinuria) almost always signifies the existence of liver dis-
ease. Both hepatocellular and cholestatic liver injury may lead to elevated serum
bilirubin levels.20,21
There are rare inherited disorders in which bilirubin excretion into the bile is
impaired, resulting in conjugated hyperbilirubinemia, namely Rotor syndrome and
Dubin-Johnson syndrome. Both conditions have a benign clinical course. The algo-
rithm for the evaluation of patients with hyperbilirubinemia is summarized in Fig. 5.

Fig. 5. Algorithm for evaluation of patients with hyperbilirubinemia.

Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
12 Woreta & Alqahtani

TESTS OF LIVER SYNTHETIC FUNCTION

The liver is the exclusive site of synthesis of albumin and most coagulation factors.
Thus, serum albumin and PT serve as true tests of hepatic synthetic function.
Serum albumin has a long half-life of about 21 days. About 4% is degraded per day.
Because of its long half-life, serum albumin levels may not be affected in acute liver
disease, such as acute viral hepatitis or drug-induced liver injury. In cirrhosis or
chronic liver disease, low serum albumin may be a sign of advanced liver disease.
However, low serum albumin is not specific for liver disease, and may occur in other
conditions, such as malnutrition, infections, nephrotic syndrome, or protein-losing
enteropathy.7
PT/international normalized ratio (INR) measures the activity of coagulation factors
II, V, VII, and X, which are all synthesized in the liver and dependent on vitamin K
for synthesis. Coagulation factors have a much shorter half-life than albumin. Thus,
PT/INR is the best measure of liver synthetic function in the acute setting. Prolongation
of the PT to more than 5 seconds above the control value (INR>1.5) is a poor prog-
nostic sign in liver disease, and an important factor in priority of liver transplantation
in model of end-stage liver disease score.
Elevation in PT/INR is also a predictor of high mortality in patients with acute alco-
holic hepatitis. Vitamin K deficiency also causes prolongation in PT, and is associated
with poor nutrition, malabsorption, and severe cholestasis with inability to absorb fat-
soluble vitamins. Administration of parental vitamin K can help distinguish vitamin K
deficiency from hepatocyte dysfunction, because it results in the correction of PT in
the case of vitamin K deficiency but not liver dysfunction.2 Table 5 summarizes the
general pattern of liver enzymes and liver function tests seen in the different categories
of hepatobiliary disease.

NONINVASIVE MARKERS OF FIBROSIS

Noninvasive tests of hepatic fibrosis have been studied extensively in many clinical
trials. Most studies of serologic markers and radiologic tests have looked at the use
of these tests for staging of fibrosis in patients with chronic liver disease.22–24
There are two general categories of noninvasive tests for fibrosis: serologic panels
of tests and radiologic tests. These include indicators of cytolysis (AST, ALT); chole-
stasis (GGT, bilirubin); hepatocellular synthetic function (INR, cholesterol, ApoA1,
haptoglobin, N-glycans); and hypersplenism caused by portal hypertension (ie,
platelet count). The most studied panels are the AST to platelet ratio, FibroTest/Fibro-
Sure (Labcorp, Burlington, USA), Hepascore (Quest Diagnostics, USA), and Fibro-
Spect (Prometheus Alb Inc., USA).
Radiologic methods for staging hepatic fibrosis are emerging as promising tools.
The methods include ultrasound-based transient elastography and magnetic reso-
nance elastography. Ultrasound-based transient elastography using a probe (Fibro-
Scan) is the most studied radiologic method for staging hepatic fibrosis. Fibroscan
was approved by Food and Drug Administration in April 2013. Using FibroScan in
United States becoming more popular as a reliable noninvasive method of assessing
liver fibrosis.

APPROACH TO PATIENT EVALUATION AND DIAGNOSIS

The first step in evaluating patients found to have liver enzyme abnormalities is to
take a careful and thorough medical history. Risk factors for viral hepatitis including
travel history, sexual practices, illicit drug use, acquisition of tattoos, body
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos

Table 5
Patterns of liver enzymes and liver function tests in various hepatobiliary diseases

Hepatobiliary Disorder Aminotransferases Alkaline Phosphatase Bilirubin Albumin Prothrombin Time

Hepatocellular
Acute [[[ (>500 IU/mL) Normal or [ to <3 times normal [ Normal Usually normal
Toxin/drug [ to >5 seconds above control value portends
Viral poor prognosis
reservados.

Ischemic
Chronic [[ (<300 IU/mL) Normal or [ to <3 times normal Normal to [ Normal or Y Often [, will not correct with parenteral
vitamin K administration
Cholestatic

Evaluation of Abnormal Liver Test

Acute Normal to [[[ Normal to [ Normal to [ Normal Normal
Chronic Normal to [[ [[[ to >4 times normal [ Normal or Y Normal or [, will correct with vitamin K
administration
Infiltrative Normal to [ [[[ to >4 times normal Normal Normal Normal

13
14 Woreta & Alqahtani

piercings, occupational exposure, and history of blood transfusions before 1990

should be ascertained. The presence of prodromal symptoms, such as nausea,
vomiting, abdominal pain, anorexia, malaise, fevers, or chills suggestive of acute
viral hepatitis, should be elicited. A history of significant weight loss raises the pos-
sibility of malignancy. Inquiry into the development of jaundice, dark urine, or light
stools is important. The acute onset of right upper quadrant pain, fever, or jaundice
suggests biliary obstruction caused by gallstones. History of pruritus suggests
cholestasis.
Clinicians should inquire about the consumption of alcohol, including frequency,
quantity, and duration. A history of obesity, diabetes mellitus, or hyperlipidemia in
the absence of significant alcohol consumption suggests the possibility of nonalco-
holic fatty liver disease. Meticulous review of the patient’s medication list and inquiry
into the use of any over-the-counter or herbal medications or nutritional supplements
should be performed. A history of inflammatory bowel disease raises the possibility of
primary sclerosing cholangitis. Finally, a family history of liver disease is important
because it suggests possible inherited liver disorders.
The physical examination is also an important diagnostic tool in the assessment of
patients with suspected liver disease. The presence of scleral icterus or jaundice
should be assessed. Hepatomegaly may be present in acute viral hepatitis, alcoholic
hepatitis, infiltrative liver disorders, or severe congestive hepatopathy caused by heart
failure. Temporal wasting and cachexia suggest advanced liver disease or malig-
nancy. Clinicians should assess for stigmata of chronic liver disease, including spider
angiomas, palmar erythema, and gynecomastia. Splenomegaly and caput medusa
suggests the presence of portal hypertension. Signs of decompensated cirrhosis
include the presence of ascites, jaundice, or asterixis/encephalopathy.
If an asymptomatic patient is found to have a first-time elevation in liver enzymes, it
is reasonable to observe the patient if (1) no risk factors for liver diseases are identified;
(2) the elevation in liver enzymes is mild (ie, less than twice the upper limit of normal);
and (3) liver synthetic function is preserved.4 Repeat testing should be performed
within 3 months. If the liver enzymes remain elevated at 3 months, work-up for liver
disease should be initiated based on the pattern of liver enzyme elevation as detailed
previously.
Liver biopsy remains the gold standard for the grading of inflammation and staging
of fibrosis in chronic liver disease, and plays an important role in determining the need
for treatment and assessing response to therapy.

SUMMARY

The routine use of serum biochemical tests allows for the detection of acute and
chronic liver injury before the onset of symptoms. These tests consist of markers of
hepatocellular injury (aminotransferases and APs); tests of liver metabolism (total bili-
rubin); and tests of liver synthetic function (serum albumin and PT). Noninvasive tests
for assessment of liver fibrosis are promising tools for diagnosis and prognosis of pa-
tients with chronic liver disease. A comprehensive history, physical examination, and
assessment of pattern of liver injury with additional laboratory and imaging testing
establish the cause of hepatobiliary disease in most cases.

ACKNOWLEDGMENTS

This work was supported by research grant from HRH Meshal Bin Abdulah Al Saud
Foundation.
Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de
ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
 Evaluation of Abnormal Liver Test 15

REFERENCES

1. Green RM, Flamm S. AGA technical review on the evaluation of liver chemistry
tests. Gastroenterology 2002;123(4):1367–84.
2. Franklin Herlong FH, Mitchell MC. Laboratory tests. In: Maddrey WC,
Schiff ER, Sorrell MF, editors. Schiff’s diseases of the liver. Wiley-Blackwell;
2012. p. 17–43.
3. Mukherjee S, Gollan JL. Assessment of liver function. In: Lok AS, Dooley JS,
Burroughs AK, et al, editors. Sherlock’s diseases of the liver and biliary system.
Wiley-Blackwell; 2011. p. 20–35.
4. Pratt DS, Kaplan MM. Evaluation of abnormal liver-enzyme results in asymptom-
atic patients. N Engl J Med 2000;342(17):1266–71.
5. Piton A, et al. Factors associated with serum alanine transaminase activity in
healthy subjects: consequences for the definition of normal values, for selection
of blood donors, and for patients with chronic hepatitis C. MULTIVIRC Group.
Hepatology 1998;27(5):1213–9.
6. Floch MH, Floch NR, Kowdley KV, et al. Netter’s gastroenterology. 1st edition.
Carlstadt (NJ): Icon Learning Systems; 2005. p. 900.
7. Longo DL, et al. Harrison’s gastroenterology and hepatology. New York: McGraw-
Hill Medical; 2010. p. 738.
8. Cohen JA, Kaplan MM. The SGOT/SGPT ratio–an indicator of alcoholic liver
disease. Dig Dis Sci 1979;24(11):835–8.
9. Diehl AM, et al. Relationship between pyridoxal 5’-phosphate deficiency and
aminotransferase levels in alcoholic hepatitis. Gastroenterology 1984;86(4):
632–6.
10. Bamford KF, et al. Serum-alkaline-phosphatase and the ABO blood-groups.
Lancet 1965;1(7384):530–1.
11. Heino AE, Jokipii SG. Serum alkaline phosphatase levels in the aged. Ann Med
Intern Fenn 1962;51:105–9.
12. Sotil EU, Jensen DM. Serum enzymes associated with cholestasis. Clin Liver Dis
2004;8(1):41–54.
13. Goldberg DM, Martin JV. Role of gamma-glutamyl transpeptidase activity in the
diagnosis of hepatobiliary disease. Digestion 1975;12(4–6):232–46.
14. Rollason JG, Pincherle G, Robinson D. Serum gamma glutamyl transpeptidase in
relation to alcohol consumption. Clin Chim Acta 1972;39(1):75–80.
15. Righetti A, Kaplan MM. Disparate responses of serum and hepatic alkaline phos-
phatase and 5’ nucleotidase to bile duct obstruction in the rat. Gastroenterology
1972;62(5):1034–9.
16. Lester R, Schmid R. Bilirubin metabolism. N Engl J Med 1964;270:779–86.
17. Robinson SH, et al. Early-labeled peak of bile pigment in man. Studies with glycine-
14C and delta-aminolevulinic acid-3H. N Engl J Med 1967;277(25):1323–9.
18. Zieve L, et al. Normal and abnormal variations and clinical significance of the
one-minute and total serum bilirubin determinations. J Lab Clin Med 1951;
38(3):446–69.
19. Weiss JS, et al. The clinical importance of a protein-bound fraction of serum bili-
rubin in patients with hyperbilirubinemia. N Engl J Med 1983;309(3):147–50.
20. American Gastroenterological Association. American Gastroenterological Associ-
ation medical position statement: evaluation of liver chemistry tests. Gastroenter-
ology 2002;123(4):1364–6.
21. Polson J, Lee WM, American Association for the Study of Liver. AASLD position
paper: the management of acute liver failure. Hepatology 2005;41(5):1179–97.

Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de

ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.
16 Woreta & Alqahtani

22. Miyake T, et al. Real-time tissue elastography for evaluation of hepatic fibrosis
and portal hypertension in nonalcoholic fatty liver diseases. Hepatology 2012;
56(4):1271–8.
23. Berzigotti A, et al. Non-invasive diagnostic and prognostic evaluation of liver
cirrhosis and portal hypertension. Dis Markers 2011;31(3):129–38.
24. Crespo G, Fernández-Varo G, Mariño Z, et al. ARFI, FibroScan, ELF, and their
combinations in the assessment of liver fibrosis: a prospective study. J Hepatol
2012;57(2):281.

Descargado para Anonymous User (n/a) en National Autonomous University of Mexico de

ClinicalKey.es por Elsevier en septiembre 08, 2021. Para uso personal exclusivamente. No se
permiten otros usos sin autorización. Copyright ©2021. Elsevier Inc. Todos los derechos
reservados.