Which is better? Guy’s versus S.T.O.N.E. nephrolithometry scoring systems in predicting stone-free status post-percutaneous nephrolithotomy

The aim of the present study was to compare the accuracy of the Guy’s and S.T.O.N.E. scoring systems in predicting percutaneous nephrolithotomy (PCNL) outcomes.

After obtaining ethics approval, medical records of patients undergoing PCNL between 2009 and 2013 at a tertiary stone center were retrospectively reviewed. Guy’s and S.T.O.N.E. scoring systems were calculated. Regression analysis and ROC curves were performed.

A total of 185 PCNLs were reviewed. The overall stone-free rate was 71.9 % with a complication rate of 16.2 %. When compared to patients with residual fragments, stone-free patients had significantly lower Guy’s grade (2.7 vs. 2; p < 0.001) and S.T.O.N.E. score (8.3 vs. 7.4; p = 0.004). Logistic regression analysis showed that both Guy’s and S.T.O.N.E. systems were significantly associated with stone-free status, OR 0.4 (p < 0.001), and OR 0.7 (p = 0.001), respectively. Furthermore, both scoring systems were significantly associated with the estimated blood loss (p = 0.01 and p = 0.005). There was good correlation between both scoring systems and operative time (r = 0.3, p < 0.001 and r = 0.4, p < 0.001) and length of hospital stay (r = 0.2, p = 0.001 and r = 0.3, p < 0.001). However, there were no significant associations between both scoring systems and complications (p = 0.7 and p = 0.6). There was no significant difference in the areas under the curves for the Guy’s and S.T.O.N.E. scoring systems (0.74 [95 % CI 0.66–0.82] vs. 0.63 [95 % CI 0.54–0.72]; p = 0.06).

Both Guy’s and S.T.O.N.E scoring systems have comparable accuracies in predicting post-PCNL stone-free status. Other factors not included in either scoring system may need to be incorporated in the future to increase their accuracy.