Urinary activity of N-acetyl-β-D-glucosaminidase (NAG) has been suggested as a marker for diabetic nephropathy. In this study, urinary activity of NAG was measured with an interval of 5 yr in 36 insulin-dependent diabetic subjects to evaluate its predictive value for development of diabetic nephropathy. During the observation period, 9 patients developed detectable signs of diabetic nephropathy. In these patients, urinary albumin concentration had increased to 503 ± 185 mg/L, compared to 16 ± 1 mg/L in patients without nephropathy (P < .01; means ± SE), and the fractional albumin excretion rate was 0.21 ± 0.07 × 10∼3, compared to 0.01 ± 0.00 × 10∼3 (P < .01). However, the activity of urinary NAG was not different in these patients compared with the patients without nephropathy (0.69 ± 0.15 and 0.61 ± 0.09 U/mmol creatinine, respectively). Furthermore, no increase in the activity of urinary NAG was seen during the observation period in either group. We concluded that the urinary activity of NAG is not related to the development of microalbuminuria and therefore cannot be used as a predictor for the development of diabetic nephropathy.

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