External validation and comparison of current scoring systems in retrograde intrarenal surgery: Multi‐institutional study with 949 patients

Objectives To externally validate and compare Resorlu‐Unsal stone score (RUSS), modified Seoul National University Renal Stone Complexity Score(S‐ReSC), Ito’s nomogram, and Retrograde Intra‐Renal Surgery (R.I.R.S.) scoring systems for predicting capabilities of both the stone‐free status and complications in a multi‐institutional study. Materials and Methods We performed a retrospective analysis of 949 patients who underwent flexible ureterorenoscopy (f‐URS) and laser lithotripsy for renal stones in two institutions between March‐2015 and June‐2020. The RUSS, modified S‐ReSC, Ito’s nomogram, and R.I.R.S. scores were calculated for each patient by the same surgeon on imaging methods. Results were compared for their predictive capability of stone‐free status and complications. Results Of 949 patients 603 were male and 346 were female with a mean age of 47.2 ± 14.3 (range 2‐84 years). Mean stone burden was 102.6 ± 42.2 (48‐270 mm 2 ). All nomograms predicted stone‐free status (Area Under Curve (AUC) were 0.689, 0.657, 0.303, and 0.690, respectively). All four scoring systems predicted complications with AUC values of 0.689, 0.646, 0.286, and 0.664 for RUSS, modified S‐ReSC, Ito’s nomogram, and R.I.R.S., respectively. Although all scoring systems were able to predict complications only Ito’s nomogram was able to predict Clavien ≥2 complications. Conclusion All four scoring systems (RUSS, modified S‐ReSC, Ito’s nomogram, and R.I.R.S.) could predict stone‐free status after f‐URS, however, the AUC values are not satisfactory in our large patient cohort. Although these scoring systems were not developed for predicting post‐operative complications, they were associated with complications in our study. However, these four scoring systems have some significant limitations. The ideal scoring system is yet to be developed.