Gamma-glutamyl transferase (GGT), also known as gamma GT, is an enzyme mainly found in the liver, but also present in the pancreas, spleen, and kidneys. Elevated levels of GGT in the blood can indicate liver or bile duct disease. When used together with ALP, another liver enzyme, GGT can help distinguish between liver and bone disease. GGT is also a useful marker for diagnosing long-term alcohol abuse, as it is often elevated in the blood of heavy drinkers.