A data-driven revision of the S.T.O.N.E. nephrolithometry score: Improved predictive accuracy for stone-free status after PCNL

ObjectiveTo improve the S.T.O.N.E. nephrolithometry scoring system by applying a factor weighting method derived from odds ratios (ORs) in logistic regression analysis for a more scientific prediction of stone-free rate (SFR) after percutaneous nephrolithotomy (PCNL).MethodsWe conducted a retrospective cohort study of 283 patients undergoing PCNL. The SFR was the primary outcome. Binary logistic regression identified independent predictors among the S.T.O.N.E. components. Statistically significant factors were assigned weighted points based on their ORs. The improved system's performance was compared to the traditional S.T.O.N.E. score using receiver operating characteristic analysis, Net Reclassification Improvement (NRI), and risk stratification based on Youden index-optimized cutoffs.ResultsStone size, obstruction, and stone density were independent predictors of SFR (all <i>p</i> < .05) and were assigned weighted scores of 2, 3, and 3, respectively, creating a revised score (range 0-11). The improved system demonstrated comparable discriminative ability to the traditional system (AUC: 0.804 vs 0.814, <i>p</i> > .05) but provided significantly superior risk reclassification (NRI = 0.233, <i>p</i> = .007). Using the Youden index-derived cutoff of 5.5, the improved system stratified patients into low-risk (scores 0-5, <i>n</i> = 123) and high-risk (scores 6-11, <i>n</i> = 160) groups. The SFR was 91.9% in the low-risk group versus 51.9% in the high-risk group (<i>p</i> < .001). This low-risk group had a significantly higher SFR than the low-risk group defined by the traditional system (91.9% vs 81.4%, <i>p</i> = .011).ConclusionThe factor-weighted S.T.O.N.E. scoring system provides enhanced clinical risk stratification for PCNL outcomes. It effectively identifies a distinct cohort of low-risk patients with a > 90% probability of stone-free success, offering improved utility for preoperative patient counseling and surgical planning.