Previous studies have explored various scoring systems using preoperative computed tomography (CT) scans to predict the postoperative stone-free rate (SFR) following percutaneous nephrolithotomy (PCNL). However, data on their applicability to retrograde intrarenal surgery (RIRS) remains limited. In this study, we aim to evaluate the predictive accuracy of five existing scoring systems for achieving stone-free status after RIRS.

We retrospectively collected all patients who underwent RIRS between January 2023 and December 2023 from one single institution. For each patient, scores were assigned with preoperative CT scan under five scoring systems (i.e., Guy's, S.T.O.N.E., CROES, R.I.R.S., SMASH). Stone free status was defined as no residual renal stones over 3mm in diameter on KUB within 1 month postoperatively. Comparison of the stone-free cohort and stone-residual cohort was performed with standard statistical methods. Areas under curves (AUC) of Receiver operating characteristic (ROC) curve was also calculated to compare the predictive value for each scoring system.

A total of 115 patients were enrolled in the study. Overall stone free rate was 60.9%. Mean Guy's, S.T.O.N.E., CROES, R.I.R.S., SMASH scores were 1.97, 6.77, 181.08, 6.61, and 12.2, respectively. AUCs of ROC curve for each scoring systems were 0.752 [95%CI: 0.661–0.843] for GUY’s score, 0.726 [95%CI: 0.627–0.825] for S.T.O.N.E score, 0.788 [95%CI: 0.702–0.874] for CROES, 0.786 [95%CI: 0.698–0.874] for R.I.R.S. scores and 0.764 [95%CI: 0.676–0.852] for SMASH scores. All scores except for GUY’s score (p=0.2597) differed between the stone-free and stone-residual cohorts. 10 patients (8.7%) received re-intervention within 6 months postoperatively.

For RIRS, All the scoring systems except for GUY’s score showed reliable predictive performance for the stone free status, while CROES nephrolithometric nomogram held the highest sensitivity.