Liver Function Tests

What are some of the most common liver function tests?

A series of special blood tests can often determine whether or not the liver is functioning properly. These tests can also distinguish between acute and chronic liver disorders and between hepatitis and cholestasis.

The most commonly performed blood tests include the following:

• Serum bilirubin test: This test measures the levels of bilirubin in the blood. Bilirubin is produced by the liver and is excreted in the bile. Elevated levels of bilirubin may indicate an obstruction of bile flow or a problem in the processing of bile by the liver.
  
• Serum albumin test: This test is used to measure the level of albumin (a protein in the blood) and aides in the diagnosis of liver disease.
• Serum alkaline phosphatase test: This test is used to measure the level of alkaline phosphatase (an enzyme) in the blood. Alkaline phosphatase is found in many tissues, with the highest concentrations in the liver, biliary tract, and bone. This test may be performed to assess liver functioning and to detect liver lesions that may cause biliary obstruction, such as tumors or abscesses.
• Serum aminotransferases (transaminases): This enzyme is released from damaged liver cells.
• Prothrombin time (PTT) test: The prothrombin time test measures how long it takes for blood to clot. Blood clotting requires vitamin K and a protein that is made by the liver. Prolonged clotting may indicate liver disease or other deficiencies in specific clotting factors.
• Alanine transaminase (ALT) test: This test measures the level of alanine aminotransferase (an enzyme found predominantly in the liver) that is released into the bloodstream after acute liver cell damage. This test may be performed to assess liver function, and/or to evaluate treatment of acute liver disease, such as hepatitis.
• Aspartate transaminase (AST) test: This test measures the level of aspartate transaminase (an enzyme that is found in the liver, kidneys, pancreas, heart, skeletal muscle, and red blood cells) that is released into the bloodstream after liver or heart problems.
• Gamma-glutamyl transpeptidase test: This test measures the level of gamma-glutamyl transpeptidase (an enzyme that is produced in the liver, pancreas, and biliary tract). This test is often performed to assess liver function, to provide information about liver diseases, and to detect alcohol ingestion.
• Lactic dehydrogenase test: This test can detect tissue damage and aides in the diagnosis of liver disease. Lactic dehydrogenase is a type of protein (also called an isoenzyme) that is involved in the body's metabolic process.
• 5'-nucleotidase test: This test measures the levels of 5'- nucleotidase (an enzyme specific to the liver). The 5'- nucleotidase level is elevated in persons with liver diseases, especially those diseases associated with cholestasis (disruption in the formation of, or obstruction in the flow of bile).
• Alpha-fetoprotein test: Alpha-fetoprotein (a specific blood protein) is produced by fetal tissue and by tumors. This test may be performed to monitor the effectiveness of therapy in certain cancers, such as hepatomas.
• Mitochondrial antibodies test: The presence of these antibodies can indicate primary biliary cirrhosis, chronic active hepatitis, and certain other autoimmune disorders.