Use of ɣ-GT activity in the diagnosis of hepatic dysfunction appears to be much more sensitive than the use of other liver enzymes, since elevation of ɣ-GT occurs earlier and lasts longer. The highest elevations are found in intrahepatic or posthepatic biliary obstruction, where values may be 5 to 30 times of normal levels. Moderately elevated ɣ-GT levels are seen in hepatitis, cirrhosis, fatty liver disease states, metastatic hepatic neoplasm, and acute or chronic pancreatitis. Increased levels of ɣ-GT are also seen in sera of heavy drinkers or patients with alcohol cirrhosis. High ɣ-GT activity is found in prostate tissue, which may account for the increased ɣ-GT activity seen in some sera from men compared with sera from women.
Szasz developed a kinetic approach in which Glupa-Carboxylat was used as the substrate; and glycylglycine, the acceptor. The use of glycylglycine accelerates the reaction greatly over the rate obtained in simple buffered medium.
GGT is often measured as a surreptitious way of screening for alcohol abuse. However, amongst alcoholics without liver disease only half show a raised GGT, the extent of which is related to neither the amount nor the duration of ethanol consumption. A large number of drugs, not just anticonvulsants, increase GGT activity, and rarely activity can be increased in carcinoma of the prostate and hyperthyroidism.
