Predicting Surgical Outcome of Percutaneous Nephrolithotomy: Validation of the Guy's Stone Score and Nephrolithometric Nomogram in Terms of Success and Complications

Abstract

This single institution retrospective study aims to validate the ability of Guy's stone score and the nephrolithometric nomogram to predict the success of PCNL and to assess the correlation of the scoring systems with the complications encountered. Material and Method: Medical files of 1646 adult patients to whom a PCNL operation was performed were reviewed. A total of 1325 patients fulfilled the needed criteria and were included in the study. Study variables were recorded from the medical files for statistical analysis. Results: Stone burden was the only pre-operative, operative and post-operative variable that had a statistically significant correlation both with success and also with the complications encountered (p< 0.05). Guy's stone score grade 1 and 2 were associated with success and grade 3 and 4 were associated with complications (p< 0.05). ASA score 3 and 4 were seen to be associated with complications (p< 0.05). Operation time > 120 minutes, presence of a staghorn stone, intra-and post-operative blood transfusion, duration of the nephrostomy catheter, Delta Hg more than 2 gr/dl and and positive post-operative urine/blood culture were the other associated variables related to the complications encountered (p< 0.05). ROC curve analysis performed to the nephrolithometric nomogram data showed that with a cut of value of 80.5% for success, the nomogram has a sensitivity of 71% and specificity of 74% (ROC AUC= 80%). The nomogram was further analyzed for an association between the complications encountered and showed that the association is not strong enough to predict a possible complication (ROC AUC= 67%). Discussion: This study shows that the nephrolithometric nomogram has a good predictive accuracy for success (AUC= 0.80) and the Guys's stone score has a good correlation both with success and with complications (p< 0.05) and can be used for pre-operative counseling and decision making.