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Minerva Urologica e Nefrologica 2020 Dec 01

DOI: 10.23736/S0393-2249.20.04055-2

Copyright © 2020 EDIZIONI MINERVA MEDICA

language: English

Development and validation of a simple stone score (SSS) to estimate the probability of residual stones prior to percutaneous nephrolithotomy

Ahmed M. HARRAZ , Ahmed R. EL-NAHAS, Mohamed A. NABEEH, Mahmoud LAYMON, Khalid Z. SHEIR, Hamdy A. EL-KAPPANY, Yasser OSMAN

Urology and Nephrology Center, Mansoura University, Mansoura, Egypt


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BACKGROUND: The purpose is to develop and internally validate a simple stone score (SSS) to estimate the probability of clinically significant residual fragments (CSRF) prior to percutaneous nephrolithotomy (PNL).
METHODS: The files of 1170 PNL procedures between January and December 2015 were evaluated. CT-derived stone characteristics were examined. Caliceal stone distribution (CSD) was assigned three grades based on the number of calices involved regardless of the renal pelvis (I: no or single calix; II: more than one calix; III: more than 2 calices or complete staghorn stones). CSRF was defined as any residuals >4 mm in postoperative CT. A logistic regression model to predict the CSRF was fitted and coefficients were used to develop the SSS. The SSS was validated by discrimination, calibration, and decision curve analysis (DCA).
RESULTS: Patients' data were split into training (936, 80%) and validating (234, 20%) datasets. In the training partition, independent predictors of CSRF were CSD-grade II (OR: 4.2; 95%CI: 2.5-7; p<0.001), grade III (OR: 7.8; 95%CI: 4.2-14.4; p<0.001) and largest stone diameter (LSD) (OR:1.3; 95%CI: 1.1-1.6; p<0.001). Score points 0, 1, 2, and 0, 3, 9 were given to LSD <30, 30- 40, >40 mm, and CSD grades I, II, III, respectively. Discrimination of the SSS was 0.79 and after 10-fold cross-validation and internal validation was 0.86. The calibration plot and DCA highlighted the validity and clinical significance of the SSS.
CONCLUSIONS: The novel SSS could be used to describe the risk of CSRF prior to PNL. Further studies are invited for external validation.


KEY WORDS: Percutaneous nephrolithotomy; Stone score; Stone-free rate; Stone complexity

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