LIVER FUNCTION TESTS
Aminotransferases (ALT/AST) :
This enzyme has two isoforms: alanine aminotransferase (ALT) and aspartate aminotransferase (AST).
Massive elevation of the serum levels of this enzyme is seen in severe viral hepatitis, hepatotoxic-induced liver injury and ischaemic liver injury.
Moderate elevations are characteristic of mild acute viral hepatitis, chronic active hepatitis, alcoholic hepatitis, cirrhosis and hepatic metastases.
Usually the ALT elevation parallels AST elevation, but in alcoholic liver disease AST elevation far exceeds that of ALT. The ratio of AST/ALT in this setting is > 2.
Alkaline phosphatase (ALP) :A striking elevation of this enzyme is seen in cholestatic disorders. Moderate and transient elevations are seen in all types of liver pathology, including hepatitis, metastatic disease and hepatic infiltrative conditions such as lymphomas, leukaemia and sarcoidosis.
Gammaglutamyl transpeptidase (GGT): The level of this enzyme correlates with that of ALP. Its level also goes up in alcoholism, diabetes mellitus, cardiac failure, pancreatic disease, fatty liver and renal failure. Elevation of the level of this enzyme is often non-specific.
Prothrombin time (PT) and international normalised ratio (INR): Elevation of the PT level and the INR is seen when hepatic synthetic function is impaired. All clotting factors except factor V are synthesised in the liver.
Serum albumin level: This marker also reflects the hepatic synthetic capacity, and hence it is low in significant liver disease.
Bilirubin: The conjugated (direct) bilirubin level is elevated in cholestasis. Unconjugated (indirect) hyperbilirubinaemia is seen in haemolysis, ineffective erythropoiesis, Gilbert’s syndrome and the rare Crigler-Najjar syndrome.
Autoimmune markers of liver disease
• Antimitochondrial antibody (AMA)—seen in primary biliary cirrhosis and autoimmune chronic active hepatitis
• Antinuclear antibody (ANA)—seen in autoimmune hepatitis
• Antismooth muscle antibody—seen in autoimmune hepatitis
• Anti-liver kidney microsomal antibody (anti-LKM)—seen in autoimmune hepatitis type II.
