GGTP

GGTP, short for gamma-glutamyl transpeptidase (also called gamma-glutamyl transferase in some texts), is an enzyme that participates in the gamma-glutamyl cycle, a pathway involved in glutathione metabolism and amino acid transport. The enzyme transfers a gamma-glutamyl group from glutathione to an acceptor molecule, facilitating the extracellular breakdown of glutathione and the uptake of amino acids by cells. GGTP is a membrane-bound enzyme found in many tissues but is most abundant in the liver, particularly on the canalicular (bile-facing) surface of hepatocytes, and it is also present in the kidney, pancreas, and intestines.

In humans, GGTP is encoded by members of the GGT gene family, with GGT1 being a major hepatic form. The enzyme exists in several isoforms and can be detected in tissue extracts as well as in serum. Clinically, serum GGTP activity is a sensitive but non-specific marker of hepatobiliary disease. Elevated levels are commonly seen in cholestasis and biliary obstruction, alcoholic liver disease, non-alcoholic fatty liver disease, and various forms of drug-induced liver injury. Because it is influenced by liver-pancreatic–biliary system function, GGTP testing is frequently interpreted alongside the alkaline phosphatase (ALP) level; a high GGTP with high ALP suggests a liver or biliary source, whereas a high ALP with normal GGTP may indicate a bone source.

Factors that can raise GGTP include excessive alcohol use and certain medications (for example, phenytoin, barbiturates, rifampin). GGTP levels are typically interpreted in the context of the overall clinical picture and other laboratory results.