Establishment and internal validation of nomogram for predicting the stone free rate of ESWL in patients with ureteral stones

Objective To develop and internally validate a nomogram for predicting the outcome of extracorporeal shock wave lithotripsy (ESWL) for ureteral stones, so as to improve the stone-free rate of ESWL for the treatment of ureteral stones. Methods It was a retrospective cohort study. A total of 286 patients who were diagnosed with ureteral stones by CT in Xuzhou Central Hospital and received ESWL between August 2019 and June 2020 were enrolled and their clinical data were collected. The outcome of ESWL was re-examined by CT within three weeks after surgery, where stone-free success was defined as no residual stones > 4 mm were detected. Their age, gender, body mass index (BMI), abdominal subcutaneous fat area, laterality, stone location, renal pelvic width, skin-to-stone distance, perinephric inflammation, stone diameter, mean stone density (MSD) and variation coefficient of stone density (VCSD) were assessed. A nomogram was developed using the significant predictors for being stone-free identified by multivariate analyses and bootstrapping was used to internally validate the nomogram. Results According to multivariate analyses, BMI, renal pelvic width, stone volume, MSD and VCSD were independent predictive factors for stone-free rate after ESWL (P<0.05). A nomogram was developed to predict the outcome of ESWL for ureteral stones based on the above five indicators. The area under the curve (AUC) of ROC in the nomogram model was 0.844. The calibration prediction curve of the nomogram for internal verification showed that the predictive calibration diagram fits well with the ideal curve. Conclusions This study develops a nomogram which can predict the ESWL outcomes of ureteric stones in a simple and practical manner.