Diagnostic value of N-acetyl-β-D-glucosaminidase for the early prediction of acute kidney injury after percutaneous nephrolithotripsy

The present observational study was undertaken in order to evaluate the diagnostic value of urinary N-acetyl-β-D-glucosaminidase (NAG) for the prediction of acute kidney injury (AKI) in patients after percutaneous nephrolithotripsy (PNL). Pre- and post-operative patient data were collected for 90 patients who underwent PNL between September 2008 and December 2010. The patients included 64 males and 26 females with an average age of 52.8±9.7 years. Pre- and post-operative urinary NAG was measured by colorimetric assay and serum creatinine levels were determined for comparative analysis. Urinary NAG levels significantly increased after PNL compared to pre-operative levels (P<0.05). AKI occurred in 11 cases after surgery. A comparison of the AKI and non-AKI groups revealed no significant differences in age, gender ratio or baseline creatinine levels (P>0.05); however, there were significant differences between the groups as regards surgical duration, post-operative infection rate, C-reactive protein levels and number of hospital days (P<0.05). NAG levels were significantly higher in the AKI compared to the non-AKI group after surgery (P<0.05). The diagnostic utility of the increase in urinary NAG 24 h after surgery was assessed by receiver operating characteristic (ROC) analysis. For an increase in NAG of 235.44%, the area under the ROC curve was 0.878 (P<0.01) and the sensitivity and specificity for AKI diagnosis were 81.8 and 91.1%, respectively. Urinary NAG significantly increased in patients suffering from AKI after surgery. This parameter is more sensitive than serum creatinine and can reflect the impairment of kidney function at an earlier stage. The surgical duration and post-operative infection rate are possible risk factors for AKI. Urinary NAG may have some clinical value in the early diagnosis of AKI after surgery.