Role of the urinary N-acetyl-beta-D-glucosaminidase/creatinine (NAG/Cr) ratio in discriminating between true and false pyuria in sterile urine bag specimens = Role of the urinary N-acetyl-beta-D-glucosaminidase/creatinine (NAG/Cr) ratio in discriminating between true and false pyuria in sterile urine bag specimens

다국어 초록 (Multilingual Abstract)

Introduction
Urethral catheterization (CATH) and suprapubic aspiration (SA) are reliable methods of collecting urine for the diagnosis of urinary tract infections (UTIs), but both are invasive and difficult. Therefore, urine collection through a sterile urine bag (SUB) is commonly used for UTI screening. However, when pyuria is found in SUB specimens, it is difficult to interpret whether this result is true or false. We aimed to determine the diagnostic performance of the urinary NAG/Cr ratio in detecting true pyuria in SUB specimens for children with suspected UTIs.
Material & Method
This retrospective study included children 2-24 months of age presenting to the pediatric emergency department (PED) and in whom urinary NAG and creatinine levels were measured and a urine culture was performed between January 1, 2018, and December 31, 2019. The diagnostic performance of the urinary NAG/Cr ratio in detecting true pyuria was identified using receiver operating characteristic (ROC) curve analysis. The optimal cutoff was calculated based on ROC curve analysis. Sensitivity, specificity, and positive and negative likelihood ratios were assessed for optimal cutoff values.
Result
Among 606 children with measured urinary NAG levels, 144 children with pyuria in SUB specimens were included in the analyses. Pyuria was consistently present in the CATH specimens of 67 (46.5%) children and absent in those of 77 (44.5%) children. The urinary NAG/Cr ratio was significantly higher in the true pyuria group than in the false pyuria group (21.5 IU/L; 95% confidence interval [CI]: 12.3-35.6; vs 9.6 IU/L; 95% CI: 6.7-16.1, P < 0.001). The area under the ROC curve (AUC) for the urinary NAG/Cr ratio was 0.776 (95% CI: 0.700-0.851). The optimal cutoff of 18.85 IU/L corresponded to the best combination of sensitivity (58.2, 95% CI: 46.4-70.0) and specificity (83.3, 95% CI: 74.7-91.6), with positive and negative likelihood ratios of 3.49 (95% CI: 2.04-5.97) and 0.50 (95% CI: 0.37-0.68), respectively.
Conclusion
The urinary NAG/Cr ratio may be a potential indicator discriminating true pyuria from false pyuria in SUB specimens in the PED. However, large prospective studies are required to implement the NAG/Cr ratio in clinical practice.