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Clinical Chemistry, Vol 36, 319-322, Copyright © 1990 by American Association for Clinical Chemistry
J Makise, E Saito, M Obuchi, M Kanayama, K Harakawa and K Yoshida
Central Clinical Laboratory, Yokosuka Kyosai Hospital, Kanagawa, Japan.
We have improved the kinetic rate assay method for determining N-acetyl- beta-D-glucosaminidase (EC 3.2.1.30; NAG) activity in urine with use of the synthetic substrate, 2-chloro-4-nitrophenyl-N-acetyl-beta-D- glucosaminide (CNP-NAG), reported previously (Clin Chem 1988;34:2140- 2). To increase the solubility of this substrate, we used crown ether (15-crown-5-ether) and ethylene glycol. In addition, we used for the standard solution NAG from human placenta, with specificity corresponding to that of human urine, so that values obtained with the CNP-NAG method and a p-nitrophenyl-NAG method ("MEI Assay NAG") correlated almost completely (r = 0.995, n = 29). Reference values for urinary NAG activity determined by the CNP-NAG method were established for untimed urine specimens from 674 healthy volunteers. The normal reference interval (mean +/- 2 SD) for NAG: 1.6-15.0 (mean 4.9) U per gram of creatinine.
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