External Validation of Modified Seoul National University Renal Stone Complexity Score to Predict Outcome and Complications of Retrograde Intrarenal Surgery: a RIRSearch Group Study.

INTRODUCTION:The Modified Seoul National University Renal Stone Complexity Score (S-ReSC) is a simple model based solely on stone location regardless of stone burden. The aims of this study were to validate S-ReSC for outcomes and complications of retrograde intrarenal surgery (RIRS) and to evaluate its predictive power against the stone burden.MATERIAL AND METHODS:Data of 1007 patients with kidney stones who had undergone RIRS were collected from our RIRSearch database. Linear-by-linear association, logistic regression, ANOVA/post hoc analysis and ROC curve (with Hanley and McNeil's test) were used for evaluation. The main outcomes were stone-free status and complications of RIRS.RESULTS:The overall stone-free rate was 76.8% (773/1007). Higher S-ReSC scores were related to lower stone-free rates and higher total, perioperative and postoperative complication rates (p<.001, p<.001, p=.008 and p<.001, respectively). S-ReSC score (p=.02) and stone burden (p<.001) were independent predictors of stone-free status. But stone burden (AUC = 0.718) had a more powerful discriminating ability than the S-ReSC score (AUC = 0.618).CONCLUSIONS:The S-ReSC score is able to predict not only stone-free status but also complications of RIRS. Although this location-only based scoring system has a fair discriminative ability, stone burden is a more powerful predictor of stone-free status after RIRS. An ideal scoring system aiming to predict outcomes of RIRS must include stone burden as a parameter.