| Background and Objective Since the first patient was treated successfully for a renal calculus with extracorporeal shock wave lithotripsy (ESWL) by Chaussy et al. in 1980, rapid acceptance and widespread use of this technique have made this form of stone therapy the first choice of therapy for most of patients with urolithiasis, and ESWL is considered a very safe and noninvasive procedure for the treatment of urolithiasis. At present, there wasn't an ideal regressive model for estimating the probability of stone-free after ESWL. This study was performed in order to investigate the prognostic factors associated with the success rate of ESWL by establishing a regressive model which was used to estimate the probability of stone-free rate after ESWL.Methods Between January, 2003 and January, 2006, a total of 366 patients (250 men and 116 women; range 4-84 years; mean age 43.05±13.13 years) with single radiopaque upper urinary tract stone underwent ESWL monotherapy with a Domier Lithotripter S. The patients with absolute contraindication for ESWL such as ureteral obstruction, pregnancy, hemorrhagic disease, severe cardiovascular or cerebrovascular disease, implanted cardiac pacemaker, morbid obesity and severe deformity of bone(s) and/or joint(s) were excluded in this study, while the patients with ureterstenosis, congenital renal anomalies and renal nonfunction were also excluded. All cases were identified by KUB/IVU or Type B ultrasonic. The results of treatment were evaluated after 3 months of follow up. Treatment success was defined as complete clearance of the stones with no residual fragments. The stone-free rate was correlated with stone features and patient characteristics using the chi square test and t-test. Factors found to be significant using the tests were further analyzed using multivariate regression analysis. Multivariate analysis was performed using a logistic regression model.Results At 3-months follow-up, the overall stone-free (success) rate was 63.4% (n=232), in these cases, 84.9% (n=197) underwent once ESWL, and 15.1% (n=35) underwent at least twice. The overall failure rate was 36.6% (n=134), in the cases, failure to disintegrate the stone was observed in 8.5% cases (n=31) and failure to clear the fragmented stone occurred in 28.1% cases (n=103). The rate of once ESWL was 86.9% (n=318), twice ESWL was 11.7% (n=43), thrice ESWL was 1.4% (n=35). According to the effect of stone clearance, two groups were divided: success group and failure group. Using the chi square test and t-test, course of disease, stone length, stone width and stone burden had a significant impact on the stone-free rate. Multivariate analysis excluded course of disease and stone burden from the logistic regression model while the other factors, such as stone length, uremia, and stone width, maintained their statistically significant effect on success rate, indicating that they were independent predictors. A logistic regression model was developed using these variables and to estimate the probability of stone-free status after ESWL. The sensitivity of the model was 90.1%, the specificity 40.3% and the overall accuracy 71.9%.Conclusions This study demonstrated that stone length is a significant independent predictor of ESWL outcome. Our regression model can predict the probability of the success of ESWL with an accuracy of 71.9%.
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