Neutrophil Gelatinase-Associated Lipocalin Biomarker and Urinary Tract Infections: A Diagnostic Case-Control Study (NUTI Study)

Objectives Acute uncomplicated urinary tract infection (UTI) in women is often treated based on symptoms alone. Urinary tract infection symptoms are highly sensitive but lack specificity and result in overuse of antibiotics. We sought to determine if urine neutrophil gelatinase-associated lipocalin (uNGAL) levels in urine can accurately discriminate between UTI and healthy women. Methods We recruited adult women aged 18 to 85 years presenting in the ambulatory setting from November 2014 to January 2016. Cases were defined as women with Centers for Disease Control and Prevention-defined UTI symptoms and a positive urine culture of more than 10⁵ organisms/mL on a midstream clean-catch specimen. Women without UTI symptoms were matched by age and menopausal status as control subjects. Exclusion criteria were no UTIs within 8 weeks, urinary tract anomalies, renal disease, pregnancy, or diabetes. Clean-catch urine samples were obtained for measuring uNGAL, prior to antibiotic treatment of cases. We used Mann-Whitney U test to compare the 2 groups. Receiver operating characteristic curves were plotted to compare the performance of uNGAL to established urinary markers. Results We enrolled 50 UTI cases and 50 control subjects. Urine NGAL levels were higher in the UTI group than in the control subjects (P < 0.0001). Using a cutoff of 23.9 ng/mL, NGAL achieved 98% sensitivity and 100% specificity. The receiver operating characteristic curve had an area under the curve of 0.97 (95% confidence interval, 0.93-1.00), which was significantly high and showed that uNGAL can identify UTI. Conclusions Urine NGAL has the potential as a biomarker for diagnosing UTIs in adult women.