Four enzymes and bilirubin are used to screen for possible liver disease.
Enzymes are proteins which facilitate chemical reactions within the body's cells. The types of enzymes within body cells vary greatly by their function and organ location. Alkaline Phosphatase (AP), Aspartate Aminotransferase (SGOT, AST), Alanine Aminotransferase (SGPT, ALT) and Gamma Glutamyl Transferase (GGT) are enzymes present in the liver cells in increased amounts. When the liver is injured, one or more of these enzymes can be released by the damaged cells causing an elevation in their blood level(s).
Many liver disorders cause damage slowly over many years in the absence of symptoms or loss of function. AP, AST, ALT and/or GGT elevations can be the only indication of a previously unrecognized chronic liver disease. Blood levels of one or more of these enzymes above the usual clinical range suggest the possibility of a liver disorder. This possibility is increased with greater elevations. For example, an enzyme elevation which is more than three times the usual clinical range is more suggestive of a liver disorder than an enzyme elevation which is less than twice the usual clinical range. Similarly, multiple enzyme elevations increase the possibility of a liver disorder.
AP, AST, ALT and GGT elevations are suggestive but not specific for liver disease. GGT elevation can also result from prolonged, excessive alcohol use. The significance of any enzyme elevation is best determined in the context of your personal medical history. Your personal physician is the best judge of the need for repeat or additional laboratory studies. Chronic viral hepatitis caused by either the hepatitis B or C virus is a significant cause of chronic liver disease in the United States. ALT elevation is more specific for liver damage caused by chronic viral hepatitis. Northwestern Mutual automatically screens blood chemistry profiles with ALT elevations for evidence of exposure to the hepatitis B and C virus.
Bilirubin is a breakdown product of hemoglobin produced in the liver and excreted in the bile. Elevated bilirubin can result from excessive red blood cell breakdown (hemolytic anemia), liver dysfunction or an obstructed bile duct. Minor elevations in bilirubin can be due to Gilbert's disease, an innocent disorder which affects 3-5% of the United States population. Like enzyme elevations, the significance of bilirubin elevation is best assessed by one's personal physician. For additional and more complete information regarding tests for liver disorders, the following websites are recommended: