Urinary N-acetyl-beta-D-glucosaminidase assay in renal transplant recipients.

Urinary N-acetyl-beta-D-glucosaminidase (NAG) activities were measured in 181 patients with renal allografts during a 15-month period. Activities were high immediately after transplantation but decreased rapidly in the absences of complication. Urinary NAG activities increased by 50% or more in relation to 33 of 36 (92%) episodes of acute rejection diagnosed and treated by clinicians during the first 90 days after transplantation. The increase preceded clinical diagnosis in 70% of the cases, the median interval being 1.5 days. NAG activities decreased after treatment of rejection in 90% of the cases. Chronic rejection, renal vein thrombosis, renal artery stenosis, oliguria, hypotension, and the administraion of gentamicin may also cause increased NAG activity. Urinary NAG assay is simple and inexpensive, and is a useful aid to the early diagnosis of rejection of renal transplants. Results must, however, be interpreted by the clinician, bearing in mind other causes for increased activity.