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Gamma-glytamyl transpeptidase is an enzyme which is found in hepatocytes and biliary epithelial cells. GGT may be high in liver disease. In particular it is a feature of biliary outflow obstruction rather than hepatocellular damage.
Note reference ranges may vary between laboratories.
GGT serum measurement provides a very sensitive indicator of the presence or absence of hepatobiliary disease. However the usefulness of measurement of serum GGT is limited by its lack of specificity. Raised GGT levels have been reported in a variety of clinical conditions including (1):
Drugs such as phenytoin and barbiturates may cause high GGT levels (2).
The reported sensitivity of a raised GGT for detecting alcohol ingestion has ranged from 52% to 94% (3,4).
The linked page GGT in hepatobiliary disease details hepatobiliary causes of a raised GGT.