Liver Function Tests

Liver function tests (LFTs) are a group of blood tests that provide important
information about the state of the liver. They measure various enzymes, proteins,
and substances that are produced, cleared, or metabolized by the liver. These tests
are not diagnostic on their own but are used in conjunction with a patient's medical
history, physical examination, and other diagnostic tests to help identify, monitor, or
rule out liver disease or damage.

Major functions of liver

1. Metabolic Functions

 Carbohydrate Metabolism:
o The liver helps regulate blood sugar levels by storing excess glucose
as glycogen (glycogenesis) and breaking down glycogen into glucose
when needed (glycogenolysis).
o It can also produce glucose from non-carbohydrate sources
(gluconeogenesis) during fasting or starvation.
 Protein Metabolism:
o The liver synthesizes many proteins, including albumin (which
maintains blood volume and pressure) and clotting factors (essential
for blood coagulation).
o It also breaks down amino acids and converts ammonia (a toxic
byproduct of protein metabolism) into urea, which is excreted by the
kidneys.
 Lipid Metabolism:
o The liver plays a key role in breaking down fats (lipolysis) and
producing cholesterol, triglycerides, and lipoproteins.
o It also helps convert excess carbohydrates and proteins into fatty acids
and triglycerides for storage.

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2. Detoxification and Waste Removal

 The liver processes and neutralizes toxins, drugs, and metabolic waste
products, making them less harmful or easier to excrete.
 It converts ammonia (a byproduct of protein metabolism) into urea, which is
excreted by the kidneys.
 The liver also metabolizes alcohol, medications, and environmental toxins.

3. Bile Production

 The liver produces bile, a fluid that aids in the digestion and absorption of
fats and fat-soluble vitamins (A, D, E, and K).
 Bile is stored in the gallbladder and released into the small intestine during
digestion.

4. Immune System Support

 The liver contains immune cells (Kupffer cells) that help filter and remove
bacteria, viruses, and other pathogens from the bloodstream.
 It also produces acute-phase proteins, which are involved in the body’s
inflammatory response to infection or injury.

5. Storage of Vitamins and Minerals

 The liver stores essential nutrients, including:

o Vitamins: A, D, E, K, and B12.
o Minerals: Iron and copper.
 These stored nutrients are released into the bloodstream as needed.

6. Synthesis of Blood Clotting Factors

 The liver produces most of the proteins required for blood clotting, including
fibrinogen and prothrombin.
 Without these factors, the blood would not clot properly, leading to
excessive bleeding.

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7. Hormone Regulation

 The liver helps regulate hormones by breaking down and excreting excess
hormones, such as insulin, estrogen, and thyroid hormones.

8. Blood Volume and Circulation

 The liver helps regulate blood volume by producing plasma proteins like
albumin, which maintain osmotic pressure and prevent fluid leakage from
blood vessels.

Functions of liver

Commonly used liver function tests typically include the followings:

1. Total Serum Bilirubin (TSB) and Bilirubin Fractions (Direct & Indirect):

 Total Bilirubin: Measures total concentration of bilirubin in blood as a

byproduct of red blood cell breakdown.

 Direct (Conjugated) Bilirubin: The bilirubin that has been processed by the
liver and is water-soluble.

 Indirect (Unconjugated) Bilirubin: The bilirubin that has not yet been
processed by the liver and is fat-soluble.

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 2. Transferase Enzymes (AST and ALT):

 Aspartate Aminotransferase (AST or sGOT):

o Found in the liver, heart, muscles, and kidneys.

o Elevated levels can indicate liver damage, but it is less specific to the
liver than ALT.

 Alanine Aminotransferase (ALT or sGPT):

o Primarily found in the liver.

o Elevated levels are more specific to liver damage, such as in hepatitis

or liver injury.

 Clinical Significance:

o AST and ALT levels are used to assess liver cell damage.
o The AST/ALT ratio can help differentiate between alcoholic liver
disease (ratio >2) and viral hepatitis (ratio <1).

3. Alkaline Phosphatase (ALP):

 Function: An enzyme found in bile ducts but also in bones.

 Clinical Significance:

o Elevated ALP levels can indicate bile duct obstruction or bone

disorders.

Further tests for assessment of liver function

1. Albumin:

 Function: Albumin is a protein produced by the liver that helps maintain

blood volume and transport hormones, vitamins, and other substances.

2. Gamma Glutamyl Transferase (GGT):

The GGT may be needed to determine if the source of elevated ALP is liver-
related.

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  Function: An enzyme found in the bile ducts.

 Clinical Significance:
o Elevated GGT levels are sensitive to bile duct problems (biliary stasis
or obstruction) and alcohol use.
o It is often used to confirm that elevated ALP is due to liver disease
rather than bone disease.

Indications of liver function tests

 When a liver disease is suspected based on clinical presentation or risk factors.

 To monitor patients with known liver disease or those on hepatotoxic
medications.
 As a part of routine health check-up in high-risk individuals (e.g., alcohol use,
obesity, hepatitis).
 In presence of Dark-Colored Urine
 In presence of Jaundice (Yellowing of Skin or Eyes)
 In presence of Fatigue, Weakness, or Unexplained Weight Loss
 In presence of Pale or Clay-Colored Stools

ALT (sGPT) & AST (sGOT)

ALT (Alanine Aminotransferase) and AST (Aspartate Aminotransferase) are

indeed transferase enzymes that play a key role in amino acid metabolism.

These enzymes are also called transferases. The GOT and GPT enzymes catalyze
the transfer of an amino group from an amino acid to an alpha-keto acid, with
pyridoxal phosphate and pyridoxamine phosphate acting as coenzymes.

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 Locations of transferases enzymes

ALT (sGPT)

ALT: alanine transaminase and is also called sGPT (serum glutamic-pyruvic

transaminase).

Function:
 ALT catalyzes the transfer of an amino group from alanine to alpha-
ketoglutarate, producing pyruvate and glutamate.
 This reaction is part of the alanine cycle, which helps transport nitrogen from
peripheral tissues to the liver for urea synthesis.
 Pyridoxal phosphate (a form of vitamin B6) acts as a coenzyme in this
reaction.

Location:

 Primary Location: Liver (highest concentration).

 Secondary Locations:
o Kidneys.
o Pancreas.
o Skeletal muscle cells.
o Red blood cells (RBCs).

ALT
L-alanine + α-ketoglutarate ⇌ pyruvate + L-glutamate
GPT

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ALT (Alanine Aminotransferase) is released into the bloodstream when liver
cells are injured or inflamed, making it a sensitive marker for liver damage.

Release of ALT in Liver Injury or Inflammation

 When liver cells (hepatocytes) are damaged or inflamed, their membranes

become permeable, allowing intracellular enzymes like ALT to leak into the
bloodstream.
 This results in elevated serum ALT levels, which are often seen in
conditions such as:
o Acute Liver Disease (e.g., viral hepatitis, drug-induced liver injury).
o Chronic Liver Disease (e.g., chronic hepatitis, cirrhosis).
o Liver Inflammation (e.g., autoimmune hepatitis, non-alcoholic
steatohepatitis).

Normal value: 7 - 56 IU/L

Definition of IU/L (International Unit per Liter)

 IU/L is a measure of enzyme activity.

 It represents the amount of enzyme that catalyzes the conversion of 1
micromole (µmol) of substrate per minute under specific conditions:
o Temperature: Usually 37°C (body temperature).
o pH: Optimal pH for the enzyme's activity.
o Substrate and Activators: Specific reagents and cofactors required
for the reaction.

High ALT level

The ALT is released into blood when the liver or the heart are damaged. Blood
ALT levels are thus elevated with liver damage (for example, from viral hepatitis)

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or with an insult to the heart (for example, from a heart attack). Some medications
can also raise ALT levels.

Causes of Elevated ALT Levels

1. Liver-Related Causes:

 Alcoholic Hepatitis:
o Chronic alcohol consumption can cause inflammation and damage to liver
cells, leading to elevated ALT levels.
 Autoimmune Hepatitis:
o The immune system attacks liver cells, causing inflammation and elevated
ALT.
 Chronic Hepatitis:
o Chronic viral hepatitis (e.g., hepatitis B or C) can cause persistent liver
inflammation and elevated ALT.
 Hepatic Necrosis:
o Severe liver cell death due to toxins, drugs, or infections can cause a sharp
rise in ALT levels.
 Cirrhosis:
o Long-term liver damage and scarring can lead to elevated ALT, though
levels may be normal or only mildly elevated in advanced cirrhosis.
 Non-Alcoholic Fatty Liver Disease (NAFLD):
o Fat accumulation in the liver can cause inflammation and elevated ALT.
 Drug-Induced Liver Injury:
o Medications like acetaminophen, statins, antitubercular drugs, and certain
antibiotics can cause liver damage and elevated ALT.
 Viral Hepatitis:
o Acute or chronic hepatitis (e.g., hepatitis A, B, C, D, or E) can cause
significant ALT elevation.
 Ischemic Hepatitis:
o Reduced blood flow to the liver (e.g., due to heart failure or shock) can
cause liver damage and elevated ALT.

2. Non-Liver-Related Causes:

 Heart Damage:
o Conditions like myocardial infarction (heart attack) or myocarditis (heart
inflammation) can cause mild ALT elevation due to heart muscle damage.

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  Pancreatitis:
oInflammation of the pancreas can sometimes lead to elevated ALT levels.
 Trauma to Striated Muscle:
o Injury to skeletal muscles (e.g., rhabdomyolysis) can cause ALT elevation,
though AST is usually more significantly elevated in such cases.
 Severe Burns:
oExtensive tissue damage from burns can lead to elevated ALT levels.
 Hemolysis:
o Breakdown of red blood cells can cause mild ALT elevation.

3. Other Causes:

 Medications:
 Systemic Infections:
 Some Metabolic Disorders:
Principle:

Alanine transaminase is measured by monitoring the concentration of pyruvate

hydrazine formed with 2,4-dinitrophenyl-hydrazine

ALT
Alanine + α-oxoglutarate L-glutamate + pyruvate
GPT

NaoH
Pyruvate + D.N.P.H Hydrazone

Brown color

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Procedure:
1- Pipette into test tube :
Reagent Sample
blank
Sample ---- 0.1ml (100 µl)
Buffer (R1) 0.5 ml (500 µl) 0.5ml (500 µl)

Mix : incubate for exactly 30 min at 37c

2,4-dintrophenylhydrazine 0.5ml (500 µl) 0.5ml (500 µl)
(R2)
Mix :allow to stand for exactly 20 min in room temperature
Sodium hydroxide (R3) 5 ml 5ml
Mix :read the absorbance of sample (A sample ) against the
reagent blank after 5 minutes , wave length 550 nm
After measure of absorbance use this table to calculate the activity of GPT enzyme
Absorbance Activity of enzyme ( IU/L)
0.025 4
0.05 8
0.075 12
0.1 17
0.125 21
0.150 25
0.175 29
0.200 34
0.225 39
0.250 43
0.275 48
0.300 52
0.325 57
0.350 62

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0.375 67
0.400 72
0.425 77
0.450 83
0.475 88
0.500 94

Compiled by Ali Abdulrasool

Reviewer: Ali Al-bayati

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 AST (sGOT)

Aspartate Transaminase (AST), also known as sGOT (serum glutamate

oxaloacetate transaminase), is an enzyme found in various tissues throughout the
body, including the liver, heart, muscles, kidneys, and brain. It plays a key role in
amino acid metabolism by catalyzing the transfer of an amino group between
aspartate and glutamate.

Aspartic acid + α-ketoglutarate oxaloacetic acid + L-glutamate

GOT

GOT (glutamate oxaloacetate transaminase), also known as AST (aspartate

transaminase), has two isoenzymes: cytoplasmic and mitochondrial. These
isoenzymes are distributed differently within cells, and their release into the
bloodstream can provide clues about the extent and type of cellular damage.
1. Cytoplasmic GOT (cGOT):
o Located in the cytoplasm of cells.
o More abundant and released more readily into the bloodstream during
mild or early cellular injury.
o Elevated levels in the blood are often seen in conditions like acute
liver injury, muscle damage, or hemolysis.
2. Mitochondrial GOT (mGOT):
o Located in the mitochondria of cells.
o Released into the bloodstream during more severe or extensive
cellular damage, as mitochondrial membranes are more resistant to
injury.
o Elevated levels are often associated with severe liver
damage, chronic liver diseases, or extensive tissue necrosis.
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Causes of Increased AST Levels:
1. Myocardial Infarction (MI)
 AST levels rise in response to heart muscle damage.
 Timing of AST elevation:
o 8 hours: AST begins to rise.
o 24–48 hours: AST peaks.
o 4–7 days: AST returns to normal.
 Note: AST is less specific for MI compared to troponins and CK-MB, which
are now the preferred biomarkers for diagnosing heart attacks.
2. Kidney Failure
 Kidney damage or failure can lead to elevated AST due to reduced clearance
of enzymes and associated tissue injury.
3. Pancreatitis
 Inflammation of the pancreas can cause AST elevation, often alongside
elevated amylase and lipase levels.
4. Gallbladder Disease
 Conditions like cholecystitis or biliary obstruction can lead to AST
elevation due to secondary liver involvement.
5. Leukemia and Lymphoma
 These cancers can cause AST elevation due to liver infiltration, hemolysis, or
muscle involvement.
Liver-Related Causes of Abnormal AST Levels:
The liver is the most common source of AST elevation because it contains high
concentrations of the enzyme. Conditions include:
• Active Cirrhosis
 Chronic liver damage leads to fibrosis and elevated AST, often with
an AST/ALT ratio > 1.
• Acute Hepatitis
 Viral hepatitis (e.g., hepatitis A, B, C) or toxic hepatitis (e.g., alcohol, drugs)
causes significant AST elevation due to hepatocyte damage.
• Liver Cancer

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  Hepatocellular carcinoma or metastatic liver cancer can elevate AST due to
tumor-related liver damage.
• Liver Trauma
 Physical injury to the liver (e.g., from accidents or surgery) releases AST into
the bloodstream.
• Autoimmune Diseases
 Conditions like autoimmune hepatitis cause immune-mediated liver
damage, leading to AST elevation.
• Genetic Disorders
 Disorders like Wilson’s disease or hemochromatosis can cause chronic liver
damage and elevated AST.
• Nonalcoholic Fatty Liver Disease (NAFLD)
 Fat accumulation in the liver leads to inflammation and AST elevation, often
associated with metabolic syndrome.
Other Causes of AST Elevation:
 Muscle Damage: Trauma, strenuous exercise, or conditions
like rhabdomyolysis can elevate AST due to muscle breakdown.
 Hemolysis: Red blood cell destruction releases AST into the bloodstream.
 Medications: Drugs like statins, antibiotics, or anticonvulsants can cause
drug-induced liver injury and AST elevation.
 Infections: Systemic infections (e.g., sepsis) can lead to multi-organ
involvement and AST elevation.
Normal value: 10- 40 U/L

Differences Between AST and ALT:

1. AST and ALT in Liver Disease
 Both AST and ALT are elevated in liver disease, but the degree of elevation
depends on the type and severity of the condition.
 In liver inflammation (e.g., acute hepatitis), levels of both enzymes can be very
high, often in the thousands (U/L).
2. Tissue Specificity
 ALT:

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 o Primarily found in the liver, making it a more specific marker for liver
injury.
o Also present in smaller amounts in muscle and red blood cells.
 AST:
o Found in the liver, heart, muscles, kidneys, and brain, making it less
specific to the liver.
3. Acute Liver Damage
 ALT rises more than AST in acute liver damage (e.g., viral hepatitis, toxic injury).
 This is because ALT is more concentrated in the liver, and its release into the
bloodstream is more pronounced during hepatocyte injury.
4. Chronic Liver Disease
 In chronic liver disease (e.g., chronic hepatitis, NAFLD), ALT is typically higher
than AST.
 However, in cirrhosis, the pattern reverses:
o AST becomes higher than ALT due to reduced ALT production by
damaged liver cells and mitochondrial AST release from fibrotic tissue.
o An AST/ALT ratio > 1 is often seen in cirrhosis, especially in alcoholic
liver disease.
Patterns of AST and ALT Elevation in Liver Disease:
Acute Hepatitis (Viral or Toxic)
 ALT > AST: ALT levels are significantly higher than AST.
 Enzyme levels can rise to 10–100 times the upper limit of normal.
Alcoholic Liver Disease
 AST > ALT: AST levels are typically 2–3 times higher than ALT.
 AST/ALT ratio is often > 2.
Nonalcoholic Fatty Liver Disease (NAFLD)
 ALT > AST: ALT is usually higher than AST, especially in early stages.
 In advanced NAFLD or NASH (nonalcoholic steatohepatitis), the AST/ALT ratio
may increase.
Cirrhosis
 AST > ALT: AST levels exceed ALT due to reduced ALT synthesis and
mitochondrial AST release.
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  AST/ALT ratio is often > 1.
Liver Cancer
 Both AST and ALT may be elevated, but the pattern depends on the extent of
liver damage and tumor involvement.
Other Considerations:
 Mild Elevations: Slight increases in AST and ALT may occur in conditions
like fatty liver, medication side effects, or mild inflammation.
 Very High Elevations: Levels in the thousands (U/L) are typically seen in acute
liver injury (e.g., viral hepatitis, drug-induced liver injury).
 Non-Liver Causes: AST elevation can also occur due to muscle injury, heart
damage, or hemolysis

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Principle:

Aspartate transaminase is measured by monitoring the concentration of oxaloacetate

hydrazone formed with 2, 4-dinitrophenyl-hydrazine

AST
L-aspartate + α-oxoglutarate L-glutamate + oxaloacetate
GOT

Pyruvate

Pyruvate + 2, 4 DNPH hydrazone

Hydrazone + NaOH hydrazone

Brown color

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Procedure:

1- Pipette into test tube :

Reagent Sample
blank
Sample ---- 0.1ml (100µl)
Buffer (R1) 0.5 ml (500µl) 0.5ml (500µl)
Mix : incubate for exactly 30 min at 37c
2,4-dintrophenylhydrazine 0.5ml (500µl) 0.5ml (500µl)
(R2)
Mix :allow to stand for exactly 20 min to room temperature
Sodium hydroxide (R3) 5 ml 5ml
Mix :read the absorbance of sample (A sample ) against the
reagent blank after 5 minutes , wave length 550 nm

After measure of absorbance use this table to calculate the activity of GOT enzyme

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 Absorbance Activity of enzyme ( IU/L)
0.020 7
0.030 10
0.040 13
0.050 16
0.060 19
0.070 23
0.080 27
0.090 31
0.100 36
0.110 41
0.120 47
0.130 52
0.140 59
0.150 67
0.160 76
0.170 89

Edited by Dr. Ail Al-bayati