Comparison of the most popular methods for predicting stonefree rate after percutaneous nephrolithotomy

Abstract

BACKGROUND: The Guy’s stone score, S.T.O.N.E. nephrolithometry, CROES nomogram, and S-ReSC scoring system have recently been externally validated as effective predictors of stone-free rate after percutaneous nephrolithotomy.

OBJECTIVE: We describe herein the advantages of identifying the most accurate scale and propose its standardized use.

MATERIALS AND METHODS: We analyzed 188 patients that underwent percutaneous nephrolithotomy for kidney stones within the time frame of October 2010 and July 2015 at a tertiary care referral center. Preoperative and postoperative non-contrast computed tomography scans were used in all patients to compare the four scoring systems, using the strict criterion of absolute absence of residual stone as the stone-free rate.

RESULTS: The overall stone-free rate was 57.9%. All scoring systems presented a statistically significant stone-free rate (p<0.001). Only the Guy’s stone score had no correlation with postoperative complications. The four scoring systems had similar accuracy, none of them were more predictive for stone-free rate than the other, and there was no significant difference in the areas under the curve between them (p=0.2). In addition, each scale had a correlation with operative time and length of hospital stay.

CONCLUSIONS: The four scales analyzed were excellent predictors for stone-free rate. They had similar receiver operating characteristic curves and areas under the curve, with no significant differences between them. However, the Guy’s stone score presented the best predictive capacity and the S-ReSC scoring system was the best method for predicting complications. It is up to the urologic community to decide which evidence-based scale is the most suitable. Meanwhile, the need for a standardized method continues to grow. 

KEYWORDS: Stone-free rate; Percutaneous nephrolithotomy; CROES; S-ReSC, S.T.O.N.E.; Guy’s stone score