Is serum γ-glutamyltransferase a misleading test?

Abstract

In the face of the widely varying factors that influence serum γ-glutamyltransferase values, it is hardly surprising that γ-glutamyltransferase estimations have not lost popularity for differential diagnosis among clinicians, even though it is one of the most sensitive indicators of hepatobiliary disease. The considerable overlap of values in many diseases coupled with the influence of so many variables on the serum enzyme activity reinforce the recent doubts that have been expressed about the clinical value of the test. Refinements to the reference ranges for serum γ-glutamyltransferase activity, together with the inclusion of serum γ-glutamyltransferase values in some discriminant function models may provide a small improvement in diagnostic value. Examination of the multiple forms of γ-glutamyltransferase activity may also yield some information about the tissue of origin of the serum activity, although methods for their characterisation have not been reliably established. It is doubtful if determination of serum total γ-glutamyltransferase activity should retain a place in the diagnostic repertoire, although a case might be made for its use in children with suspected biliary tract disease. In most cases the serum transaminase activity remains the best indicator of mild hepatocellular damage and blood alcohol concentrations of alcoholism. It seems an appropriate time for laboratories performing γ-glutamyltransferase estimations to re-examine the requests for this test and assess whether the results are clinically useful.