Reduced renal allograft survival is related to low urinary N-acetyl-beta-D-glucosaminidase excretion during the first posttransplant month

Abstract

The excretion of urinary N-acetyl-beta-D-glucosaminidase (NAG) was measured daily between day 7 and day 28 in 33 renal allograft recipients enjoying an entirely uncomplicated first postoperative month. Graft status was evaluated after 4 and 6 years and related to NAG excretion. After 4 years, 6 patients had experienced graft loss due to chronic rejection. Posttransplant urinary NAG excretion in the group of patients with failing grafts was significantly lower (9.4 +/- 6.3 vs. 17.2 +/- 8.5 U/g urinary creatinine, P = 0.036). Univariant analysis of recipient and donor characteristics revealed urinary NAG excretion to be the only parameter significantly differing between the groups. After 6 years, a total of 8 patients had lost their grafts. The posttransplant urinary NAG excretion in this group was 10.8 +/- 6.2 U/g; in the 25 patients with functioning grafts NAG excretion was 17.4 +/- 8.8 U/g (P = 0.064). A very low urinary NAG excretion ( < 7 U/g) was seen in 5 patients and associated with poor graft survival after 4 and 6 years (odds ratios 12.5 (1.9-82.1) and 6.9 (1.1-44.8), respectively. Kaplan-Meier analysis showed a reduced graft survival in this subgroup (P = 0.031). Receiver operating characteristics (ROC) analysis demonstrated an association between low NAG excretion and graft survival rates both at 4 and 6 years (area under the ROC curve 0.799 +/- 0.115, P, 0.05, and 0.747 +/- 0.104, P < 0.05, respectively). Cox proportional hazards analysis identified a low urinary NAG excretion as an independent prognostic risk factor. Urinary NAG excretion was expressed as unit per gram of urinary creatinine; as the amount of NAG excreted depends on the graft mass, and the amount of urinary creatinine depends on the recipient body mass, a low NAG excretion (in terms of U/g urinary creatinine) could be a surrogate marker of an unfavorable low graft to body weight ratio, which, in turn, might be associated with a reduced graft survival.