GGT is elevated by ingestion of large quantities of alcohol (needs reference)  However, determination of high levels of total serum GGT activity is  not specific to alcohol intoxication, and the measurement of selected serum forms of the enzyme offer more specific information. Isolated elevation or disproportionate elevation compared to other liver enzymes (such as ALT or alanine transaminase) can indicate harmful alcohol use or alcoholic liver disease, and can indicate excess alcohol consumption up to 3 or 4 weeks prior to the test.  The mechanism for this elevation is unclear. Alcohol might increase GGT production by inducing hepatic microsomal production, or it might cause the leakage of GGT from hepatocytes.