A prospective, observational study to evaluate the efficacy of the retrograde intrarenal surgery scoring system for predicting stone-free rate following retrograde intrarenal surgery

ABSTRACT Introduction: Retrograde intrarenal surgery (RIRS) is widely performed for renal calculi; however, stone-free outcomes vary according to the stone burden and intrarenal anatomy. The RIRS scoring system was developed to objectively predict the stone-free rate (SFR) using preoperative computed tomography (CT) parameters. This study prospectively evaluated its predictive performance. Methods: In this prospective, observational study, 100 consecutive patients undergoing RIRS at a tertiary center (August 2023–March 2025) were included. Preoperative CT urography assessed stone number, cumulative diameter, density (hounsfield unit), location, renal infundibulo-pelvic angle (RIPA), renal infundibular length (RIL), and renal infundibular width (RIW). Each case received a RIRS score (4–10). Stone-free status (SFS) was assessed at 4 weeks; residual fragments >2 mm were considered failure to achieve SFS. Logistic regression identified the predictors of non-SFS and receiver operating characteristic analysis evaluated diagnostic performance. Results: The overall SFR was 78%. SFR declined with increasing score: 100% (4–5), 96% (6), 55.6% (7), 9% (8), and 0% (9–10) (P < 0.001). Larger stone burden, higher density, acute RIPA, longer RIL, narrower RIW, and higher RIRS score were significantly associated with failure to achieve SFS on the univariate analysis. The score demonstrated good discrimination (area under the curve ≈ 0.76). At a cutoff of 5, sensitivity was 51.3%, specificity was 100%, positive predictive value was 100%, negative predictive value was 36.7%, and accuracy was 62%. Conclusions: The RIRS scoring system enables effective preoperative risk stratification, accurately identifying low-risk patients with a high likelihood of clearance and high-risk cases at risk of failure, thereby supporting surgical planning and patient counseling.