Correlation between urinary activity of N-acetyl-beta-D-glucosaminidase (NAG) and albumin excretion rate in type II (non-insulin-dependent) diabetic subjects.

Different kidney diseases are often associated with high urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG), a lysosomal enzyme involved in the breakdown of glycoproteins, whose activity is also increased in diabetic patients with poor metabolic control or vascular complications. In order to evaluate the relationship between renal function and urinary NAG levels in diabetes mellitus, 30 type II diabetic patients without evidence of kidney disease and 18 control subjects were studied. In each subject 24-h urinary excretion rates of NAG (fluorimetric method), albumin and beta 2-microglobulin (radioimmunoassay), together with 51Cr-EDTA clearance were performed. In diabetic patients urinary levels of NAG (356 +/- 25 vs 162 +/- 9.2 nmol/h/mg creatinine, p less than 0.0001) and albumin (21 +/- 2.5 vs 4.3 +/- 0.5 mg/24h, p less than 0.0001) were significantly higher than in the controls, while beta 2-microglobulin levels and 51Cr-EDTA clearance did not differ in the two groups. Moreover in diabetic patients NAG and albumin levels were positively and significantly correlated (r = 0.63, p less than 0.001). These results suggest that urinary NAG excretion rate may be altered early in diabetic patients with apparently normal renal function; its diagnostic value seems to be similar to that of the albumin excretion rate.