External Validation and Predictive Accuracy Assessment of Guy's Stone Score as a Preoperative Tool for Estimating Percutaneous Nephrolithotomy Outcomes

To externally validate Guy's stone score system and estimate its predictive accuracy. An analysis of 282 consecutive patients, who underwent a percutaneous nephrolithotomy, was performed. The association between Guy's stone score and several pre-, intra-, and postoperative parameters was assessed. A univariate and multivariate analysis was conducted to identify the independent predictors for stone-free rates. Area under the curve was used for predictive accuracy estimation. Stone burden, multiple stone locations, number of stones, number of implicated caliceal groups, and Guy's stone score were significantly associated with stone-free outcomes. The multivariate analysis showed that Guy's stone score, number of stones, and number of implicated caliceal groups are independent predictors of stone-free status. Receiver operating characteristic curve analysis revealed a significant predictive accuracy for the Guy's stone score. The present study externally validated Guy's stone score. Significant predictive ability combined with great predictive accuracy was found.