REACT-UTI: A 72-Hour Composite to Predict Early Non-Response and Length of Stay in Hospitalized Adults with Lower Urinary Tract Infection—A Prospective Observational Study

<b>Background and Objectives:</b> Early bedside tools that flag non-response in hospitalized adults with lower urinary tract infection (UTI) could align clinical care with antimicrobial stewardship. We evaluated REACT-UTI, a 72 h composite combining C-reactive protein (CRP) clearance ≥35%, defervescence (temperature < 37.5 °C), and ≥2-point symptom improvement, to predict early non-response and hospital length of stay (LOS), and we assessed modifiable processes of care. <b>Methods:</b> We conducted a prospective observational study of adults with culture-confirmed lower UTI (n = 126) admitted to a tertiary hospital in Timișoara (December 2023-August 2025). The primary outcome was 72 h early clinical response (ECR) defined by REACT-UTI. Multivariable logistic regression examined associations of catheter-associated UTI (CAUTI), time-to-effective therapy, baseline CRP, diabetes, early catheter removal/exchange (≤48 h), and early intravenous-to-oral switch (≤72 h) with non-response. <b>Results:</b> Overall, 76/126 patients (60.3%) achieved ECR. Non-responders more often had CAUTI, higher baseline CRP, longer time-to-effective therapy, ESBL or fluoroquinolone-resistant <i>Enterobacterales</i>, and longer LOS (14.1 vs. 9.8 days; <i>p</i> < 0.001). Adjusted models showed that CAUTI, delayed active therapy, higher baseline CRP, and diabetes increased the odds of non-response, whereas early catheter removal (adjusted odds ratio [aOR] 0.5, 95% confidence interval [CI] 0.3-0.9) and early IV-to-oral switch (aOR 0.4, 0.2-0.8) were protective. Greater CRP clearance correlated with shorter LOS (ρ = -0.52; <i>p</i> < 0.001). <b>Conclusions:</b> In this single-center setting with a high burden of antimicrobial resistance, REACT-UTI at 72 h identified patients at risk of early non-response and prolonged hospitalization and highlighted actionable levers-timely active therapy, catheter management, and early oral step-down. External validation in diverse settings is needed before broader implementation.