GGT - (Gamma glutamyl transferase)

Gamma-glutamyltransferase (GGT) also known as gamma glutamyl transpeptidase (GGTP);is a well-established serum marker for alcohol-related liver disease. However, GGT's predictive utility applies well beyond liver disease: elevated GGT is linked to increased risk to a multitude of diseases and conditions, including cardiovascular disease, diabetes, metabolic syndrome (MetS), and all-cause mortality. The primary role of cellular GGT is to metabolize extracellular reduced glutathione (GSH), enabling precursor amino acids to be assimilated and re-utilized for synthesis of intracellular GSH. Serum GGT is therefore a marker of oxidative stress which leads to depletion of GSH.

Largest amounts of this enzyme are found in the kidney, with smaller accumulations in the liver and heart. It is a microsomal enzyme, but levels are frequently elevated in patients with liver disease characterized by stasis of bile flow. GGT is also elevated in patients with acute hepatocellular injury and in alcoholics while it is not elevated during pregnancy. A major value of this test is in confirmation of the significance of elevated levels of alkaline phosphatase. High levels of ALP activity in serum arise from hepatobiliary disease, bone disease, and  transient hyperphosphatasaemia in children. The value of the γ-GT activity is often useful to differentiate, whether an elevation of ALP activity comes from the liver or the bones; high levels of both suggest liver origin.