Nomogram and scoring system for predicting stone-free status after extracorporeal shock wave lithotripsy in children with urolithiasis.

ABSTRACT

OBJECTIVE: To determine the stone-free rate after extracorporeal shock wave lithotripsy (ESWL) and its associated factors to formulate a nomogram table and scoring system to predict the probability of stone-free status in children. PATIENTS AND METHODS: A total of 412 children (427 renal units [RUs]) with urolithiasis were treated with ESWL using a lithotriptor between 1992 and 2008. Cox proportional hazards regression was used to model the number of treatment sessions to stone-free status as a function of statistically significant demographic characteristics, stones and treatment variables. A bootstrap method was used to evaluate the model's performance. Based on the multivariate model, the probabilities of being stone-free after each treatment session (1, 2 and >3) were then determined. A scoring system was created from the final multivariate proportional hazard model to evaluate each patient and predict their stone-free probabilities. RESULTS: Complete data were available for 395 RUs in 381 patients. Of the 395 RUs, 303 (76.7%) were considered to be stone-free after ESWL. Multivariate analysis showed that previous history of ipsilateral stone treatment is related to stone-free status (hazard ratio [HR] 1.49; P = 0.03). Stone location was a significant variable for stone-free status, but only in girls. Age (HR 1.65, P = 0.02) and stone burden (HR 4.45, P = 0.002) were significant factors in the multivariate model. CONCLUSION: We believe that the scoring system, and nomogram table generated, will be useful for clinicians in counselling the parents of children with urolithiasis and in recommending treatment.