Gamma-glutamyltransferase (GGT)

GGT is an enzyme that has a role in the transport of amino acids into cells and in glutathione metabolism. The highest activity is found in the kidney (but damage to the kidneys leads to leakage into the urine rather than plasma) and hence most of the GGT in plasma comes from the liver. The plasma activity of GGT is often used as an adjunct to alkaline phosphatase as an indicator of hepatobiliary disease.

Common causes of isolated elevated GGT

Ethanol
Drugs eg phenytoin
Fatty liver - obesity, diabetes, hyperlipidaemia

GGT is requently elevated with alkaline phosphatase . However, it is not normally elevated in pregnancy (alkaline phosphatase is released from the placenta) nor does it change with growth in childhood (alkaline phosphatase is released from bone). GGT is a useful marker of any hepatobiliary dysfunction in these cases.

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