External Validation and Comparison of Nephrolithometric Scoring Systems Predicting Outcomes of Retrograde Intrarenal Surgery.

Introduction: Preoperative assessment of renal stones is essential to selecting treatment options and achieving high success rates; thus, some nephrolithometric scoring systems have been developed by using preoperative clinical data and stone characteristics. Initially, nomograms predicting stone-free rates (SFRs) were designed for percutaneous nephrolithotomy. After this, some were modified, and new scoring systems were developed for retrograde intrarenal surgery (RIRS). In this study, we aimed at validating and comparing the accuracy of four scoring systems predicting the SFR of RIRS. Materials and Methods: We conducted a prospective study. The data of 110 consecutive patients who required RIRS for renal stones between May 2018 and February 2020 were evaluated. The patients were divided into four groups regarding total score: 0, 1, 2, ≥3 according to the Resorlu-Unsal Stone Score (RUSS). The scores were calculated between 5 and 15 for the size of the stone, topography or location, degree of obstruction of the urinary system, number of stones, and evaluation of Hounsfield units (S.T.O.N.E.) scoring system. Modified Seoul National University Renal Stone Complexity (S-ReSC) scores of the patients were between 1 and 12. Finally, the patients were classified between 4 and 10 points with the R.I.R.S. scoring system. Results: The mean RUSS, S.T.O.N.E., R.I.R.S., and modified S-ReSC scores were 1.14 (±0.818), 10.78 (±1.499), 6.50 (±1.305), and 2.29 (±1.710), respectively. The area under curve values of RUSS, S.T.O.N.E., R.I.R.S., and S-ReSC were 0.735 (95% confidence interval [CI] 0.623-0.826), 0.725 (95% CI 0.626-0.823), 0.752 (95% CI 0.646-0.857), and 0.755 (95% CI 0.660-0.849), respectively. Logistic regression analysis revealed that the RUSS was an independent predictive factor for SFR (p = 0.028). Conclusion: The results showed that all four scoring systems predict the SFRs for RIRS accurately. However, surgeons should prefer RUSS when all four nomograms are available, except when assessing single renal stones. In that case, S-ReSC should be used for assessment. Three other nomograms except the S.T.O.N.E. scoring system can be suitable for the assessment of lower caliceal stones.