Focus: Biochemistry, an Overview on Gamma Glutamyl Transferase

Volume 2 Issue 5 May, 2012

Consultation Liaison Psychiatry

Gamma Glutamyl Transferase (GGT) has long been known to be helpful in Psychiatry to detect recent consumption of alcohol, as this information can be useful during motivational interview in alcohol de-addiction. However knowledge about GGT can be of help to physicians across specialities. GGT is a microsomal glycoprotein enzyme present in hepatocytes and biliary epithelial cells, renal tubules, pancreas and intestine. It is also present in cell membrane performing transfer of glutamyl residues to various peptide acceptors and involved in glutathione metabolism. Serum GGT activity mainly attributed to hepatobiliary system even though it is found in more concentration in renal tissue.
The normal level of GGT is 9 to 85 U/L.

GGT as Diagnostic tool

Elevated serum GGT activity can be found in diseases of the liver, biliary system, and pancreas. In this respect, it is similar to alkaline phosphatase (ALP) in detecting disease of the biliary tract. The main value of GGT over ALP is in verifying that ALP elevations are, in fact, due to biliary disease; ALP can also be increased in certain bone diseases, but GGT is not.

Elevated serum GGT levels of more than 10 times is observed in alcoholism. It is partly related to structural liver damage, hepatic microsomal enzyme induction or alcoholic pancreatic damage. But GGT is a poor marker when alcohol consumption needs to be screened in patients with non-alcoholic liver diseases or in hospitalized patients. Serum GGT may help to distinguish those with or without liver disease. Small increase is observed in fatty liver in alcoholics. Raised level of GGT must be interpreted in the context of other liver function tests.

• Mild liver disease tends to result in a ratio of alanine transaminase (ALT) to aspartate transaminase (AST) of greater than 1.
• More extensive liver disease tends to result in an ALT to AST ratio of less than 1.
• In a patient who is known to abuse alcohol; if the AST and ALT are normal then the GGT may provide an indicator of recent alcohol intake.
• Alcohol cessation and relation to GGT.
• Increased activities usually return to normal if the patient abstains from alcohol with a normalization time of 2-3 weeks.
• Persistently abnormal values in the absence of continuing ethanol exposure suggest liver disease.

GGT and risk of disease

GGT has long been used as a liver function test and a marker of alcohol abuse but in recent years, knowledge about the physiological function and several important associations have been expanded.

• Many epidemiological studies have proved that GGT is an independent predictor of risk of diabetes, hypertension, metabolic syndrome, coronary disease and hypertension.
• GGT is a novel predictor of chronic kidney disease.
• In Cancer- GGT, a known marker for apoptotic balance, seems to promote tumour progression, invasion and drug resistance.
• GGT can also be an early marker of oxidative stress.

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