The gamma-glutamyl transferase (GGT) test may be used to determine the cause of elevated alkaline phosphatase (ALP). Both ALP and GGT are elevated in disease of the bile ducts and in some liver diseases, but only ALP will be elevated in bone disease. GGT is more responsive to biliary obstruction than are aspartate aminotransferase (AST)/ (SGOT) and alanine aminotransferase (ALT) /(SGPT).GGT discriminates the source of elevated ALP. It is utilized as a supplementary test to be sure that the elevation of ALP is indeed coming from the liver or biliary tract. In contrast to the ALP, GGT is not elevated in diseases of bone, placenta or intestine.GGT is markedly increased in lesions that cause intrahepatic or extrahepatic obstruction of bile ducts. GGT can be used to screen for chronic alcohol abuse (it will be elevated in about 75% of chronic drinkers) and to monitor for alcohol use and/or abuse in people who are receiving treatment for alcoholism or alcoholic hepatitis.