Urinary N-acetyl-beta-D glucosaminidase (NAG) level in idiopathic nephrotic syndrome

Urinary N-acetyl-beta-D: glucosaminidase (NAG) is a sensitive biomarker of renal parenchymal disease. The aim of this study was to investigate variations in the levels of NAG excretion among different sub-groups of nephrotic syndrome (first episode, relapsers, and resistant) and its prediction based on proteinuria. Thirty-five patients with idiopathic nephrotic syndrome, aged 1-12 years, as well as 15 age- and gender-matched normal children (controls) were enrolled in the study. Among the 35 patients, ten were classified with first episode nephrotic syndrome (FENS), 17 with relapsing nephrotic syndrome (RNS), and eight with steroid-resistant nephrotic syndrome (SRNS). Urinary NAG/creatinine levels were significantly increased in SRNS patients as compared to FENS and RNS patients (p < 0.001); the FENS and RNS groups had comparable levels. A urinary NAG/creatinine value of ≤108.9 U/g was found to identify steroid-sensitive patients with a sensitivity, specificity, positive predictive value, and negative predictive value of 78.8, 100, 100 and 77.7%, respectively. Significant correlations were found between experimental and predicted values of urinary NAG/creatinine in steroid sensitive nephrotic syndrome (SSNS) (R (2) = 0.9643) and SRNS patients (R (2) = 0.9823). Urinary NAG/creatinine values were found to be higher in SRNS than SSNS patients and have moderate predictive value for steroid responsiveness. This level can be obtained based on urinary protein/creatinine ratio or 24 h urinary protein levels.