Abstract
Objective: To evaluate the responsiveness of the Recurrent Urinary Tract Infection Symptom Scale (RUTISS) to antibiotic treatment and determine the minimal clinically important difference (MCID). Methods: Female adults with recurrent UTI (N = 108, mean age = 53.6 years) completed a repeated-measures, longitudinal, 40-day naturalistic follow-up study. For participants initiating and completing antibiotic treatment within this period, RUTISS scores were evaluated at baseline (2 days pre-treatment), day 1 of treatment, day 3, and at follow-up (7 days post-treatment). Responsiveness was assessed using effect sizes pre-and post-treatment (rank-biserial correlation), Spearman's rank correlations with anchor measures (Patient Global Impression of Change, PGIC, and UTI Symptom Assessment, UTISA), and receiver operating characteristic analysis. The MCID was triangulated via anchor-and distribution-based methods. Results: The RUTISS total score demonstrated excellent responsiveness between all timepoints and was strongest between baseline and day 3 (rank-biserial r = 0.52), with strong correlations with the PGIC (Spearman's rho = 0.73) and UTISA (Spearman's rho = 0.63). Receiver operating characteristic analysis indicated excellent discrimination for detecting even minimal improvement (AUC = 0.82). The recommended MCID was 6.5 points, exceeding the standard error of measurement. All subscales demonstrated good to excellent responsiveness. Conclusion: The RUTISS demonstrates excellent responsiveness to antibiotic treatment providing a validated MCID, enabling precise interpretation of treatment effects. As the first fully validated PROM for recurrent UTI, the RUTISS addresses a critical unmet need to assess patient symptom reporting. By providing a responsive and interpretable patient-centered endpoint, the RUTISS enables adequately powered clinical trials and evidence-based symptom monitoring, directly supporting improved patient care and intervention development.