Serum gamma-glutamyl transpeptidase in chronic extrahepatic cholestasis.

Studies in the literature have shown the inhibitory action of bilirubin on serum gamma-glutamyl transpeptidase (GGT) activity. In spite of this, GGT is a sensitive diagnostic indicator, comparable to alkaline phosphatase for the diagnosis of chronic extrahepatic cholestasis (CEHC). To evaluate the relationship of bilirubin, alkaline phosphatase (AP) activity and GGT activity in CEHC we studied 30 patients with CEHC divided into two groups: A, 14 male and female subjects with serum bilirubin levels of 2 to 10 mg/dl, and B, 16 male and female subjects with serum bilirubin levels of 10.1 to 44 mg/dl. Serum GGT activity was measured by diluting serum samples 1:5 and 1:10. GGT values were equivalent in the two groups, there was no correlation between bilirubin and GGT (r = +0.179, P less than 0.01), and there was a significant correlation between GGT and AP (r = +0.627, P less than 0.01). The present results show that, if GGT inhibition by bilirubin did occur, this inhibition was not sufficient to prevent the increase in serum GGT levels and that the sensitivity of GGT as a marker for CEHC is similar to that of alkaline phosphatase.