Diagnostic significance of some urinary enzymes for detecting acute rejection crises in renal-transplant recipients: alanine aminopeptidase, alkaline phosphatase, gamma-glutamyltransferase, N-acetyl-beta-D-glucosaminidase, and lysozyme.

We compared the diagnostic validity of five urinary enzymes--alanine aminopeptidase (EC 3.4.11.2), alkaline phosphatase (EC 3.1.3.1), gamma-glutamyltransferase (EC 2.3.2.2), N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30), and lysozyme (EC 3.2.1.17)--as indicators of acute rejection crises in renal-transplant recipients. In 82 patients (group A), the excretion of each of these five enzymes was measured daily from transplantation until discharge from hospital. In another 69 patients (group B), enzyme determinations were made when the patient came for regular checkups (about every four to eight weeks). We used an "activity ratio" (the activity measured at a particular time compared with the activity on the preceding determination) value of 1.5 as the decision point. In group A, use of this discrimination point for alanine aminopeptidase, gamma-glutamyltransferase, and N-acetyl-beta-D-glucosaminidase yielded a specificity and sensitivity of about 90%. In group B, only alanine aminopeptidase had a greater diagnostic sensitivity than creatinine alone. Evidently, measurement of alanine aminopeptidase can be a helpful indicator of acute rejection crises, when interpreted in combination with other available relevant clinical, biochemical, and immunological data.