Novel prediction scoring system for simple assessment of stone-free status after flexible ureteroscopy lithotripsy: T.O.HO. score

OBJECTIVES To develop a novel simple quantitative scoring model for predicting stone-free status after a flexible ureteroscopy lithotripsy procedure by standardizing the complexity of ureteral stone characteristics. METHODS We retrospectively reviewed 586 patients with renal or ureteral stones who underwent flexible ureteroscopy lithotripsy at Abiko Toho Hospital, Chiba, Japan, from 2015 to 2018. Multivariate regression was applied to examine the relationship between preoperative descriptors and stone-free status, and a nomogram was developed using significant predictors. Next, the individual components of the nomogram were assigned points to form a simple scoring system. The predictive performance of this new scoring system was compared with the STONE score at optimal cut-off values using receiver operating characteristic curve and area under the curve analyses. RESULTS Multivariate logistic regression findings showed that factors associated with stone-free status were length, Hounsfield unit and stone location. A nomogram prediction model was developed with an area under the curve value of 0.845, then consequently used to develop a new simple score system termed the T.O.HO. score consisting of three stone characteristics: (T)allness (1-5 points), (O)ccupied lesion (1-3 points) and (HO)unsfield units evaluation (1-3 points). The T.O.HO. score was significantly higher in stone remaining (7.66) than stone-free (5.27; P