Performance of the Quadruple-D Score Versus Other Nephrolithometric Tools in Obese Patients Undergoing Percutaneous Nephrolithotomy.

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.