Which is a Better Predictor for the Safety and Efficacy of Retrograde Intrarenal Surgery; Stone Size or Volume? A Study of RIRsearch Study Group

<b><i>Objective:</i></b> To compare the predictive effects of stone size and volume on the efficacy and safety of retrograde intrarenal surgery (RIRS) and to determine the cutoff values of stone volume for prediction of RIRS efficacy and safety. <b><i>Methods:</i></b> Patients who underwent RIRS between 2017 and 2021 in six referral centers were retrospectively included in the study. The database of the RIRsearch group, which was formed prospectively, was used for this retrospective analysis. The surgical results and complications of RIRS were evaluated according to stone size and stone volume and compared between these groups. <b><i>Results:</i></b> A total of 1128 patients were included. Operation time, intraoperative complication rate, and postoperative complication rate increased significantly as stone size and stone volume increased (<i>P</i> < .05). Stone size and volume were significant indicators for stone-free rates, but pairwise comparison showed that stone volume was a significantly better predictor of surgical success compared with stone size (<i>P</i> < .001). Stone size was not sufficient to predict postoperative complications, whereas stone volume predicted these complications with low performance. <b><i>Conclusions:</i></b> Stone volume was a better predictor for surgical success than stone size, and it was as reliable as stone size in predicting postoperative complications.