Rearrangement of the Guy’s stone score improves prediction of stone-free rate after percutaneous nephrolithotomy

Özet

Objective: We propose a modification of the original Guy´s Stone Score (GSS) to hold on 20 % of prognosticdiscrimination among groups which makes this score a more reliable resource for risk assessment in patientsundergoing percutaneous nephrolithotomy (PCNL).Material and methods: Historical cohort of 126 patients undergoing PCNL from December 2010 to November2014 was included in the survey. Every patient was classified according to the original GSS. For thenew classification of Guy Stone Score (GSS-M) all of the subgroups included in the scale were analyzedindividually and then ranked from better to worst according to the postoperative stone- free rates (SFRs).This ranking led us to reclassify all the original subgroups, clustering them in three new categories accordingto their SFRs as subgroups of good, intermediate and poor prognosis, trying to achieve at least 20% ofprognostic discrimination among the groups.Results: Hundred and twenty-six PCNL procedures were evaluated, but only 124 were included for statisticalanalysis and classified based on SFR according to the GSS as follows: 76% for grade 1, 71% for grade 2,55% for grade 3 and 20% for grade 4. The SFRs were also assessed for the GSS-M obtaining the followingpredictive values as 93%, 67% and 44% for the good, intermediate and poor prognostic groups, respectively.The prognostic difference among the GSS-M groups was always >20% (p<0.05).Conclusion: The original GSS has limitations to predict SFR because of its poor discrimination poweramong prognostic groups. This rearrangement improves prediction of SFR and better discriminates riskgroups in PCNL.