Urinary Interleukin-8 (IL-8) and Neutrophil Gelatinase-Associated Lipocalin (NGAL) as Rapid Biomarkers for Distinguishing Symptomatic Urinary Tract Infection from Asymptomatic Bacteriuria: A Prospective Diagnostic Accuracy Study

Urinary tract infection (UTI) is the most prevalent bacterial infection globally; however, differentiating symptomatic UTI from asymptomatic bacteriuria (ASB) remains a significant diagnostic challenge for vulnerable populations like pregnancy women, elderly as well as patients with diabetes. Current urine culture, the gold-standard test, is time consuming and is unable to distinguish active infection from colonisation. ObjectivesThis prospective diagnostic accuracy study assessed whether urinary interleukin-8 (IL-8) and neutrophil gelatinase-associated lipocalin (NGAL) could serve as rapid biomarkers to differentiate between symptomatic UTI vs ASB. Methods 320 adult patients with suspected UTI were recruited from a tertiary care hospital over the period of 12 months. Clinical criteria and quantitative urine culture (≥10⁵ CFU/mL) were used to classify participants as symptomatic UTI (n = 210) and ASB (n = 110). Urinary levels of IL-8 and NGAL were measured by ELISA. Receiver operating characteristic (ROC) curves were used to evaluate diagnostic performance. Symptomatic UTI had significantly greater median levels of urinary IL-8 (285 pg/mL vs. 42 pg/mL; p < 0.001) and NGAL (156 ng/mL vs. 38 ng/mL; p < 0.001) than ASB infection. The area under the ROC curve (AUC) for IL-8 was 0.94 (95% CI: 0.91–0.97), and using a cutoff value of 120 pg/mL, sensitivity was 91%, specificity was 88%. AUC of NGAL was 0.92 (95% CI: 0.88–0.95), while using a cutoff of 85 ng/mL provided a sensitivity and specificity of 89%140 and 85%,138 respectively. The combination of both biomarkers increased sensitivity to 95% and specificity to 91%. Compared with serum biomarkers, additional advantages of urinary IL-8 and NGAL are their rapid detection method and and/or availability at early time points (within a few hours after sampling), which can help find ways to prevent unnecessary antibiotic prescriptions while improving clinical decision making in urine tract infection management.