To investigate the influencing factors of one-stage stone-free rate of flexible ureteroscopic lithotripsy in the treatment of upper urinary tract calculi of cumulative diameter >2 cm and establish a stone-free prediction model.

From January 2016 to July 2021, the clinic data of the 182 cases of upper urinary tract calculi of cumulative diameter >2 cm were collected, including preoperative data, CT value, stones location, cumulative diameter, pelvis and lower calyceal funnel angle < 30°, operation time, hospital stay, postoperative complications and one-stage stone-free rate. The independent factors affecting the stone-free rate were analyzed and a combined prediction model was established.

All 182 patients completed the operations. Multivariate regression analysis showed that the independent risk factors were urinary tract infection, stone location (subrenal calyx calculi), pelvis and lower calyceal funnel angle <30°, stone cumulative diameter. The formula of combined predictors was as follows: L=urinary tract infection+1.263×stone location (lower calyceal stone)+1.290×angle between renal pelvis and lower calyceal funnel <30°+5.611×cumulative stone diameter. The area under the ROC curve of the combined predictor and each independent influencing factor in predicting positive for postoperative stone residue was as follows: combined predictor (0.898) > cumulative stone diameter (0.811) > stones location (subrenal calyx calculi ) (0.650) > urinary tract infection (0.608) > pelvis and lower calyx funnel angle <30°(0.588). The maximum value of Youden index was 0.660, the corresponding sensitivity was 0.813, and the specificity was 0.847. The maximum Youden index was assosciated with a combined predictor of 13.21, a cut off value above which postoperative prediction was made and residual stones will be positive.

Flexible ureteroscopy lithotripsy is a safe and feasible method for the treatment of upper urinary tract calculi of cumulative diameter >2 cm. The formula of combined predictors was obtained by combining the independent factors and the combined predictors higher than the critical value of 13.21 would indicate residual positive postoperative stones.