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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.