Feasibility of Stone Recurrence Risk Stratification Using the Recurrence of Kidney Stone (ROKS) Nomogram

Purpose: We sought to assess the performance of the Recurrence of Kidney Stones nomogram for risk stratification of recurrence in a retrospective study. Materials: and Methods: We performed a case-control study of 200 patients (100 with and 100 without subsequent recurrence) who underwent kidney stone surgery between 2013-2015, with at least 5 years of follow-up. We analyzed the performance of the 2018 ROKS nomogram via area under the receiver operating curve (ROC-AUC) for predicting 2- and 5-year stone recurrence. We evaluated the nomogram’s ability to stratify patients based on low or high risk of recurrence at: a) an optimized cutoff threshold (i.e. optimized for both sensitivity and specificity), and b) a sensitive cutoff threshold (i.e. high sensitivity (0.80) and low specificity). Time-to-recurrence data were estimated using the Kaplan Meier method. Results: : The ROKS nomogram demonstrated fair ability to predict recurrence at 2 and 5 years (ROC-AUC of 0.67 and 0.63, respectively). At the optimized cutoff threshold, recurrence rates for the low and high-risk groups were 20 % and 45% at two years, and 50% and 70% at five years, respectively. At the sensitive cutoff threshold, the corresponding recurrence rates for the low and high-risk groups was of 16% and 38% at two years, and 42% and 66% at five years, respectively. Kaplan-Meier analysis revealed a significant recurrence-free advantage between the groups for both cutoff thresholds (p<0.01, Fig. 2). Conclusions: : The ROKS nomogram could serve as a tool for recurrence risk stratification into lower and higher risk groups and facilitate adherence to risk-based follow-up protocols.