Original Article Novel prediction scoring system for simple assessment of stone-free status after flexible ureteroscopy lithotripsy: T.O.HO. score Shunsuke Hori, 1,2 Hideo Otsuki, 2 Kei Fujio, 2 Hideyuki Kobayashi, 1 Koichi Nagao, 1 Koichi Nakajima 1 and Yozo Mitsui 1 1 Department of Urology, Faculty of Medicine, Toho University, Tokyo, and 2 Department of Urology, Abiko Toho Hospital, Chiba, Japan Abbreviations & Acronyms ASA-PS = American Society of Anesthesiologists-Physical Status AUC = area under the curve BMI = body mass index CI = confidence interval CT = computed tomography ESWL = extracorporeal shockwave lithotripsy HU = Hounsfield unit OR = odds ratio PCNL = percutaneous nephrolithotomy ROC = receiver operating characteristic STONE = (S)ize, (T) opography, (O)bstruction, (N)umber of stones and (E)valuation of HU T.O.HO. = (T)allness, (O) ccupied lesion and (HO) unsfield units evaluation URL = ureteroscopy lithotripsy Correspondence: Yozo Mitsui M.D., Ph.D., Department of Urology, Faculty of Medicine, Toho University, 5-21-16 Omorinishi, Ota-ku, Tokyo 143- 8540, Japan. Email: mitsui@med.shimane- u.ac.jp Received 22 January 2020; accepted 18 May 2020. 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 < 0.001) cases. The area under the curve for the T.O.HO. score was 0.833 at an optimal cut-off value of 7, whereas that for the STONE score was 0.683 at an optimal cut-off value of 9, showing the superiority of this new scoring system. Conclusion: The T.O.HO. score is a useful tool for predicting stone-free status in patients who have undergone a flexible ureteroscopy lithotripsy procedure. Key words: flexible ureteroscopy lithotripsy, predictor, stone-free, ureteroscopy lithotripsy, urolithiasis. Introduction Urolithiasis is one of the most frequently diagnosed urological diseases, and its prevalence is increasing throughout the world, including Japan. 1,2 Treatment for affected patients includes medication, ESWL, URL and PCNL, which are selected individually based on a variety of factors, including various characteristics of the calculus, patient preference and physician expertise. Although PCNL remains the first-line standard procedure for patients with renal stones >20 mm in diameter or multiple stones, recent technological improvements in visual- ization and laser technology have enabled the choice of a URL procedure for even proximal and intrarenal stones of relatively large size. 3,4 For example, Xu et al. reported that favorable therapeutic effects could be obtained even in patients with a cumulative renal stone burden >40 mm by use of flexible URL with a holmium laser. 5 As a result, URL is increasingly being used for treatment of urolithiasis, even when the stones are relatively large, a trend that is likely to continue. In recent years, several stone scoring systems have been developed to standardize the com- plexity of urolithiasis, with multiple studies carried out to show putative predictors of patient © 2020 The Japanese Urological Association 1 International Journal of Urology (2020) doi: 10.1111/iju.14289