Gamma glutamyl transpeptidase (GGT)
Gamma glutamyl transpeptidase or GGT is an enzyme produced in the bile ducts. Measurement of the GGT is an extremely sensitive test and may be elevated in many types of liver disease. Many drugs, including alcohol, cause an elevation of the GGT, and its activity may be increased in heavy drinkers even in the absence of liver damage or inflammation. An important feature of GGT is that it can detect the presence of alcohol, even after a small amount of alcohol is ingested. Thus, the GGT test is important in the evaluation and management of alcoholism.
Because GGT is not increased in bone disease or bone growth, it can help differentiate liver disease from skeletal disease when the ALP is elevated. Both the ALP and the GGT are increased in a number of diseases that affect bile drainage, such as gallstones, tumors blocking the common bile duct, alcoholic liver disease, or drug induced hepatitis that blocks the flow of bile in smaller channels within the liver. However, the ALP is found in other organs and tissues, such as the bone, the placenta, and the intestinal tract. Therefore, the GGT is used as supplementary test to verify that an elevated ALP is due to disease or injury to the liver or biliary tract, rather than disease affecting other organs.
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The GGT is elevated in bone disease as well as in liver disease.