Diagnosing Urinary Tract Infection in Young Febrile Children in the Emergency Department.

Importance: Diagnosing urinary tract infection (UTI) in preverbal, pre-toilet trained children is challenging and may lead to unnecessary testing and treatment. UTICalc estimates UTI risk using clinical and laboratory data but has not been prospectively validated. Objectives: To prospectively validate UTICalc version 3.0 for predicting UTI and to evaluate its utility in guiding clinical decisions. Design, Setting, and Participants: This prospective diagnostic study was conducted at 2 tertiary care pediatric emergency departments (EDs) in Canada from November 2022 to January 2025. Children aged 2 to 24 months presenting with measured fever (≥38.0 °C) were enrolled. Exclusions included congenital urinary tract abnormalities, immunosuppression, current antimicrobials, or prior enrollment. Participants were followed up to identify UTIs; urine culture results were reviewed within 48 hours, and phone or email follow-up was completed within 2 weeks for those without testing at the index visit. Exposure: UTICalc-predicted probability of UTI. Main Outcomes and Measures: The primary outcome was UTI, defined as positive urinalysis and significant uropathogen culture growth. The primary analysis examined discriminative performance using area under receiver operating characteristic curve (AUROC). Secondary analyses included calibration (calibration plots, slope, Brier score) and clinical utility (net benefit analysis, comparison with clinician practice). Results: Among 2561 included participants (1212 [47%] female; 1326 [64%] younger than 12 months), 111 children (4%) were classified as having a UTI. In the full sample, 2256 (88.1%) had urine testing and/or provided follow-up data. The clinical model AUROC was 84.1% (95% CI, 80.4%-87.9%). At a 2% UTI risk threshold, sensitivity was 96.4%, and specificity was 34.1%; at a 5% risk threshold, sensitivity was 82.0%, and specificity was 73.8%. The clinical and dipstick model AUROC was 95.3% (95% CI, 93.3%-97.4%), with 94.0% sensitivity and 86.9% specificity at 5% risk. The sensitivity and specificity for clinicians were 98.2% and 57.3%, respectively. Calibration slopes were 0.11 (95% CI, 0.09-0.13) and 0.06 (95% CI, 0.05-0.07) and Brier scores were 0.04 (95% CI, 0.03-0.05) and 0.05 (95% CI, 0.04-0.06) for the clinical and clinical and dipstick models, respectively. Decision curve analysis showed both models were associated with positive net benefit across a range of risk thresholds. Conclusions and Relevance: In this cohort study of 2561 febrile children aged 2 to 24 months presenting to the ED, UTICalc showed strong diagnostic performance, especially with dipstick results. While it did not outperform experienced clinicians, it offered a useful, evidence-based adjunct for guiding urine testing decisions, supporting efficient care in the pediatric ED.