External validation of the T.O.HO. score and derivation of the modified T.O.HO. score for predicting stone-free status after flexible ureteroscopy in ureteral and renal stones

Abstract The T.O.HO. scoring system was developed to predict stone-free status after flexible ureterenoscopy (fURS) lithotripsy applied for ureter and renal stones. This study aimed to perform the external validation of the T.O.HO. score in the Turkish population and propose a modification for this system. Material Methods Patients who underwent fURS for kidney and ureteral stones between January 2017 and January 2020 were retrospectively analyzed. The patient and stone characteristics and perioperative findings were noted. The T.O.HO. score was externally validated and compared with the STONE score. Stone-free parameters were evaluated with the multivariate analysis. Based on the results of this analysis, the T.O.HO. score was modified and internally validated. Results A total of 621 patients were included in the study. The stone-free rate was determined as 79.8% (496/621) after fURS. The regression analysis showed that stone area had better predictive power than stone diameter (p=0.025). Lower pole (reference), middle pole [odds ratio (OR)=0.492 p=0.016] and middle ureteral (OR=0.227, p=0.024) localizations, stone density (OR=1.001, p<0.001), and stone volume (OR = 1.008, p <0.001) were determined as independent predictive markers for stone-free status. Based on the effect size of the stone surface area in the nomogram, stone volume was divided into five categories, at 1-point intervals. The AUC values of the T.O.HO., STONE, and modified T.O.HO. score in predicting stone-free status were calculated as 0.758, 0.634, and 0.821, respectively. The modified T.O.HO. created by adding stone volume was statistically significantly superior to the original version (ROC curve comparison, p < 0.001). Conclusion The T.O.HO. score effectively predicted stone-free status after fURS. However, Modified T.O.HO. SS showed the best predictive performance compared with original T.O.HO. SS.