Gamma GTGGT · Gamma-glutamyl transferase
A liver enzyme that is sensitive to alcohol and to bile flow problems.
Gamma-glutamyl transferase is an enzyme concentrated in the liver and bile ducts. When liver cells are irritated or bile drainage is obstructed, more of it leaks into the blood, so it is used as a liver marker.
It matters mainly for what it can distinguish. A raised alkaline phosphatase can come from either liver or bone; if gamma GT is raised alongside it, the liver is the more likely source. It is also the liver enzyme most responsive to regular alcohol intake, which is why it appears on so many panels.
In practice it is read with ALT, AST and alkaline phosphatase rather than alone. It can sit mildly above the range in people with no liver disease at all, and a single raised value is a prompt to look at the pattern rather than a diagnosis.