Liver function tests

A groups of blood tests that give information about the state of a liver.

These tests include prothrombin time (PT/INR), aPTT, albumin, bilirubin (direct and indirect), and others.

The liver transaminases aspartate transaminase (AST or SGOT) and alanine transaminase (ALT or SGPT) are biomarkers of liver injury in a patient with some degree of intact liver function.

Some blood tests are associated with functionality (e.g., albumin), some with cellular integrity (e.g., transaminase), and some with conditions linked to the biliary tract (gamma-glutamyl transferase and alkaline phosphatase).

Several biochemical tests are used in the evaluation and management of patients with hepatic dysfunction.

Total bilirubin

Alanine transaminase (ALT)

Aspartate transaminase (AST)

AST/ALT ratio

Alkaline phosphatase (ALP)

Gamma glutamyl transpeptidase (GGT)

15′ Nucleotidase


Alpha-fetoprotein (AFP)

Coagulation test

Serum glucose

Lactate dehydrogenase


Reference range in adults Total bilirubin, Unconjugated bilirubin, Conjugated bilirubin mg/dL 0.1-1.0,0.2-0.7, 0.1-0.4

Measurement of total bilirubin includes both unconjugated (indirect) and conjugated (direct) bilirubin.

Unconjugated bilirubin is a breakdown product of heme.

The liver is responsible for clearing the blood of unconjugated bilirubin, by conjugating it, to make it water-soluble through an enzyme named UDP-glucuronyl-transferase.

When the total bilirubin level exceeds 1.5 mg/dL indicates liver disease.

When total bilirubin level exceeds 3.5 mg/dL bilirubin desposition at the sclera, skin, and mucous membranes will give these areas yellow color, thus it is called jaundice.

The increase in predominantly unconjugated bilirubin is due to overproducion, reduced hepatic uptake of the unconjugated bilirubin and reduced conjugation of bilirubin.

Overproduction can be due to reabsorption of hematoma and ineffective erythropoiesis that increased red blood cell destruction.

Gilbert’s syndrome and Crigler-Najjar syndrome have defects in UDP glucuronyl transferase defect, affecting bilirubin conjugation.

The degree of rise in conjugated bilirubin is directly proportional to degree of hepatocyte injury.

Viral hepatitis can also causes the rise in conjugated bilirubin.

In parenchymal liver disease and incomplete extrahepatic obstruction, the rise in conjugated bilirubin is less than the complete common bile duct obstruction due to malignant causes.

In Dubin-Johnson syndrome, a mutation in multiple drug-resistance protein 2 (MRP2) causes a rise in conjugated bilirubin.

In acute appendicitis, total bilirubin can rise.

In pregnant women, the total bilirubin level is low in all three trimesters.

When the total serum bilirubin increases over 95th percentile for age during the first week of life for high risk babies, it is known as hyperbilirubinemia of the newborn and requires light therapy to reduce the amount of bilirubin in the blood.

Hemolytic jaundice is the commonest cause of pathological jaundice.

Babies with Rh hemolytic disease, ABO incompatibility with the mother, Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency and minor blood group incompatibility are at increased risk of getting hemolytic jaundice.

Alanine transaminase (ALT) is found in high concentrations in liver?

Alanine transaminase is found in kidneys, heart, and muscles.

Alanine transaminase catalyses the transamination reaction, and only exist in cytoplasmic form.

Any kind of liver injury can cause the rise in ALT.

A rise up to 300 IU/L is not specific to liver, but can be due to the damage of other organs such as kidneys or muscles.

When ALT rises to more than 500 IU/L, causes are usually from the liver, and can be due to hepatitis, ischemic liver injury, and toxins that causes liver damage.

The ALT levels in Hepatitis C rises more than in Hepatitis A and B.

Persistent ALT elevation of more than 6 months duration is known as chronic hepatitis.

ALT elevations are associated with alcoholic liver disease, Non-alcoholic fatty liver disease (NAFLD), and steatohepatitis, reduced insulin responsive,reduced glucose tolerance, increased free fatty acids and triglycerides.

ALT levels in pregnancy are elevated in conditions such as hyperemesis gravidarum was, pre-eclampsia and HELLP syndrome.

Caffeine consumption can reduce the risk of ALT elevation in individuals who drink alcohol, are overweight, have impaired glucose metabolism, or viral hepatitis.

Aspartate transaminase (AST) reference range is

0-35 IU/L.

AST exists in two isoenzymes: mitrochondrial form and cytoplasmic form.

AST highest concentrations are in the heart, followed by liver, muscle, and kidney.

Mitrochondrial AST elevations suggest tissue necrosis in myocardial infarction and chronic liver disease.

More than 80% of the liver AST activity is contributed by mitochondrial form of the isoenzyme.

Circulating AST in blood is contributed by the cytoplasmic form of AST.

AST is esepecially elevated in cirrhosis.

In certain pregnancy conditions such as hyperemesis gravidarum, pre-eclampsia, and help syndrome, AST can be elevated.

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