AN IMPROVED METHOD FOR EVALUATION OF NEPHROTOXICITY BY ASSAY OF URINARY beta N -ACETYL--D-GLUCOSAMINIDASE (NAG) ACTIVITY

Reaction conditions of N-acetyl- beta -D-glucosam inidase (EC 3.2.1.30;NAG) determination in untreated urine samples were studied, using 4-nitrophenyl-Nacetyl- beta -D-glucosaminide (PNP-NAG) as substrate. Final concentrations of 8 mm ol of PNP-NAG, 25 m mol of acetate, or 100 mm ol of citrate (pH 4.80 at 37 C) per liter and a sample/ reagent volum e ratio of 1/ 8 were found to be optimum. The within-run and between-run precision was excellent, with CVs averaging 2.67 and 4.55%, respectively. Reference values for urinary NAG activity assayed by this m ethod were established for untimed hum an urine specimens from 206 healthy subjects. The normal reference interval (mean- 1SD) was 0.15-15.05 (4.51 - 3.02) U per gram creatinine. By this method, urinary NAG activity can be m easured over a wide range (up to 200 U/ L) in untreated urine samples with high sensitivity. Urine samples need no pretreatment, and two reagent solutions are enough for measurement of NAG activity. The method is thus suitable for use with various automated analyzers. Finally, this m ethod requires only to 25 muL of untreated urine. Therefore, it is appropriate for evaluating nephrotoxicity in hum an (especially neonates and infants) and sm all animal models by assay of urinary NAG activity.