Gamma-glutamyltransferase (GGT) is a membrane-bound enzyme found in the sinusoidal membranes of the liver cell.

Although the GGT level cannot reliably identify heavy drinkers, when elevated in drinkers in the absence of other known causes it is likely to be alcohol related. However elevated GGT levels may sometimes occur without an obvious explanation.

An increased GGT level in heavy drinkers is thought to be related to:

• enzyme induction ( possibly as a protective effect on the liver)
• liver cell death associated with chronic consumption may result in release of GGT enzyme into the bloodstream

GGT as a marker of liver damage is also supported by:

• the finding that GGT is predictive of increased alcohol-related morbidity
• the association of elevated GGT with increased mortality in middle-aged men

Elevated GGT levels may also be an indicator of toxic effects of alcohol on systems that cannot be so easily measured. For example, in comparison with normal levels of GGT, the top decentile GGT level has been associated with:

• increased rates of fractures
• more surgical consultations
• with increased sick absenteeism
• neuropsychologic impairment

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