Performance of the Quadruple-D score versus other nephrolithometric tools in obese patients undergoing percutaneous nephrolithotomy.

Abstract

Objective: To evaluate whether the CT-based Quadruple-D score predicts stone-free status after percutaneous nephrolithotomy (PCNL) in obese patients and to compare it with established nephrolithometric scores, including SCR, CROES, Guy's Stone Score, and S.T.O.N.E.

Methods: We retrospectively analyzed obese adults (BMI > 30 kg/m²) who underwent PCNL at a tertiary center between January 2013 and June 2025 and had preoperative non-contrast CT and 1-month postoperative imaging. The Quadruple-D score (0-4) assigned one point each for stone volume <500 mm³, attenuation <1000 HU, skin-to-stone distance <100 mm, and non-lower calyceal single-site distribution. Stone-free status was defined as no residual fragment >4 mm. Comparative statistical and ROC analyses were performed.

Results: Among 104 patients, 56 were stone-free and 48 were not. Age, sex, BMI, ASA class, laterality, and hydronephrosis were similar between groups (all p > 0.05). Stone-free patients had smaller stones (20.0 vs 29.5 mm, p = 0.001) and lower stone burden (293.0 vs 587.0 mm², p = 0.001). SCR (98.8 ± 4.9 vs 74.9 ± 12.3, p = 0.001) and CROES (212.7 ± 41.1 vs 146.0 ± 55.8, p = 0.001) were significantly higher in the stone-free group. Guy's Stone Score was also associated with stone-free status (p = 0.001), whereas S.T.O.N.E. showed weaker significance (p = 0.028). Quadruple-D did not differ between groups (p = 0.581) and showed poor ROC performance.

Conclusion: In obese patients undergoing PCNL, SCR, CROES, and Guy's Stone Score were useful predictors of stone-free outcomes, whereas the Quadruple-D score had limited predictive value.