Gamma-glutamyltransferase is a reliable marker for tubular effects of contrast media.

The aim of this study was to evaluate the usefulness of the measurement of urinary excretion of the brush-border enzyme gamma glutamyl-transferase (GGT), in comparison with that of alanine aminopeptidase (AAP), as a marker for tubular toxicity due to contrast media (CM). Urinary activities of AAP and GGT were measured prior to the administration of CM and 1, 3 and 5 days after in forty-nine adult renal patients undergoing a radiological examination with intravascular administration of CM. The behavior of GGT was similar to that of AAP. In fact, urinary activities of both AAP and GGT increased greatly after CM. This effect was maximal on the 1st day and statistically significant for both enzymes. Furthermore, on the 1st day a relevant increase of enzyme activity (at least +50% over the basal value) was observed in the same number of patients (67%) for AAP and GGT. The concordance between GGT and AAP variations was high and statistically significant. Finally, different variables (osmolarity, dose of CM, and baseline renal function of the patients) had a similar effect on urinary excretion of AAP and GGT. The repeatability of duplicated determinations of GGT resulted better than that of AAP. In conclusion, the good concordance of the results of GGT with those of AAP justifies the use of GGT as a marker for tubular effects due to CM. Furthermore, the measurement of GGT has a better repeatability than that of AAP.