Factors Associated with Stone-Free Outcome after Retrograde Intrarenal Surgery Using Low-Energy Holmium YAG Laser Based on Multivariable Logistic Regression
Anupong Sawasdee, MD¹, Kittisak Chumpong, PhD²
Affiliation : ¹ Department of Surgery, Sichon Hospital, Nakhon Si Thammarat, Thailand; ² Division of Computational Science, Faculty of Science, Prince of Songkla University, Songkhla, Thailand
Background: Retrograde intrarenal surgery (RIRS) has become an established minimally invasive treatment for kidney stones, particularly in cases where extracorporeal shockwave lithotripsy or percutaneous nephrolithotomy are unsuitable. However, stone-free (SF) outcomes vary, and identifying preoperative factors associated with success remains essential for improving patient selection and surgical planning.
Objective: To identify factors associated with SF outcomes after RIRS and to develop a simple model-based clinical decision rule using preoperative variables.
Materials and Methods: The present study was a retrospective study that included 114 patients who underwent RIRS. Baseline characteristics were compared between SF and non-stone-free (non-SF) groups. All variables were screened using bivariate logistic regression, and those with significant results were included in a multivariable analysis. Model performance was evaluated using standard statistical measures, and a simple decision rule was constructed from key preoperative factors.
Results: Stone diameter was independently associated with SF outcomes (AOR 0.86, 95% CI 0.76 to 0.98, p=0.024). Prior open surgery (AOR 0.09, 95% CI 0.01 to 1.21, p=0.070) and log-transformed estimated blood loss (AOR 0.29, 95% CI 0.07 to 1.11, p=0.071) showed borderline associations. The final model demonstrated good discriminative performance (AUC 0.87) and acceptable calibration (Hosmer-Lemeshow, p=0.47). A simple decision rule incorporating kidney stone diameter and surgical history stratified patients into low- and high-risk groups, with residual fragment rates of 12.0% and 33.7%, respectively.
Conclusion: Preoperative factors, particularly stone diameter and prior surgical history, play a key role in SF outcomes after RIRS. A simple clinical rule based on these variables may support risk stratification and guide patient counseling in routine practice.
Received 29 September 2025 | Revised 21 November 2025 | Accepted 24 November 2025
DOI: 10.35755/jmedassocthai.2026.1.03494
Keywords : Retrograde intrarenal surgery; Stone-free rate; Renal calculi; Clinical decision rule; Multivariable logistic regression
