The liver regulates many important metabolic functions of the body. Injury to the liver results in the disruption of these functions. The severity of liver damage can be assessed by liver function tests.
Total protein is composed of albumin and globulin, and is produced mainly in the liver. Elevated levels of protein can be found in chronic liver disease, dehydration, chronic infection and alcoholism. Severe liver disease, malnutrition and chronic renal failure can result in low level of protein.
The liver produces albumin. Severe liver disease impairs the production of albumin to a low level. A reduced level can also be found in kidney disease due to excess excretion in the urine. A decrease in serum albumin level is also found in conditions of impaired synthesis such as malnutrition, malabsorption, liver disease and other chronic diseases.
Globulins have an active role in the immunological mechanisms and act as a transport system for various substances. Elevated levels of globulins indicate the presence of chronic illnesses or infections. Grossly elevated levels are seen in multiple myeloma, which is a type of cancer.
Bilirubin is a yellow pigment, which is produced by the breakdown of RBCs and excreted by the liver. Bilirubin level will rise when the liver is unable to conjugate and excrete it. This occurs when there is excessive breakdown of RBCs or when there is liver damage due to hepatitis infection or chronic liver disease. Hence this test helps in the diagnosis of liver disease, investigation of anaemia due to excessive breakdown of RBCs and in assessing the degree of jaundice.
Alkaline phosphatase is an enzyme found in the bone, liver, intestine, placenta and kidney. It is present at high concentrations in children with rapid bone growth. Elevated levels can also be found in liver diseases and some types of bone disease.
Aspartate Aminotransferase (AST / SGOT)
AST is an enzyme widely distributed in high concentrations in the liver, heart, muscle and kidney. It rises to a peak 36 hours after a heart attack and returns to normal after three or four days. High levels of the enzyme can also be found in liver disease and muscle disease.
Alanine Aminotransferase (ALT / SGPT)
The liver tissue is rich in this enzyme. Damage to the liver causes large amounts of the enzyme to be released into the blood stream. Hence high levels of ALT can be found in liver disease such as acute hepatitis.
Gamma Glutamyltransferase (GGT)
This liver enzyme is released in large amounts into the blood stream when there is damage or injury to the liver. Elevated level of the enzyme is associated with liver damage resulting from liver disease and excessive alcohol consumption.