Is serum gamma-glutamyltransferase a misleading test?

Although it is now 30 years since the discovery of y-glutamyl transferase (EC 2.3.2.2.), the clinical relevance of a raised activity of the enzyme in serum remains controversial. The use of the enzyme as a potential diagnostic aid did not emerge until the early 1960s, when it was introduced as a new test of liver function.1 2 Further work since then suggests that serum y glutamyltransferase activity may be a sensitive index of hepato biliary dysfunction,3 and the early prediction that measurement of y-glutamyltransferase activity would be established in the laboratory repertoire seems to have been fulfilled.4 The associa? tion between excessive alcohol consumption and raised activities of serum y-glutamyltransferase, particularly in the absence of other abnormal results of biochemical tests of liver function, was made in the early 1970s, and a serum y-glutamyltransferase estimation has been included in many screening programmes to detect an excessive intake of alcohol.5 6 It is rare, however, to find a biochemical test that is both tissue specific and disease specific, and y-glutamyltransferase activity appears to be no exception. The serum activity of the enzyme has been shown to be affected by several factors and to rise in various clinical conditions. Also its induction by a wide variety of drugs, including alcohol, makes interpretation of test results difficult. Consequently, the claimed advantage of its sensitivity is marred by its lack of specificity. Recently, doubts