Synonyms

   Transpeptidase, Gamma-Glutamyl

Clinical Significance

   It is useful for

       Diagnosing and monitoring hepatobiliary disease, it is currently the most sensitive enzymatic indicator of liver disease

       Ascertaining whether observed elevations of alkaline phosphatase are due to skeletal disease (normal gamma-glutamyltransferase: GGT) or reflect the presence of hepatobiliary disease (elevated GGT)

       A screening test for occult alcoholism

Specimen

   Serum

Stability

   Refrigerated (preferred) : 7 days

   Frozen : 365 days

   Ambient : 7 days

Reference Range

   Male : 8-61 U/L

   Female : 5-36 U/L

Interpretation

   An elevation of gamma-glutamyltransferase (GGT) activity is seen in any and all forms of liver disease, although the highest elevations are seen in intra- or posthepatic biliary obstruction. Elevated values can also indicate alcoholic cirrhosis or individuals who are heavy drinkers. The finding of increased GGT and alkaline phosphatase (ALP) activity is consistent with hepatobiliary disease. The finding of normal GGT activity and increased ALP activity is consistent with skeletal disease.

Limitation

   Gamma-glutamyltransferase activity is inducible by drugs such as phenytoin and phenobarbital and, therefore, elevations should not be considered indicative of liver disease until drug use is ruled out. Elevations are also seen after ingestion of alcoholic beverages. In very rare cases, gammopathy, in particular, type IgM (Waldenstrom macroglobinemia) may cause unreliable results.