Assay of N-Acetyl-β-D-Glucosaminidase in Urine from Neonates: Comparison of Two New Colorimetric Methods Using MNP-GlcNAc and VRA-GlcNAc as Substrates

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The NAG activity present in urine from newborn babies was assayed using two colorimetric procedures with either MNP-GlcNAc or VRA-GlcNAc as substrate and compared with data obtained with the well established PNP-GlcNAc procedure. Both new assays were easy to perform and reproducible. The MNP-GlcNAc method has the advantage that it is now available as a kit; however, the VRA-GlcNAc procedure is more sensitive. NAG activity, creatinine concentration and NAG-index values were determined in normal neonates and within-run imprecision calculated. Excellent correlations were found between MNP-GlcNAc-ase and VRA-GlcNAc-ase indices (r = 0.984) and between PNP-GlcNAc-ase and VRA-GlcNAc-ase indices (r = 0.952). When low molecular weight urinary components were removed by gel filtration no significant change in VRA-GlcNAc-ase activity was observed.