Retrograde Intrarenal Surgery (RIRS) is recommended for the treatment of renal stones smaller than 20 mm. The Stone Management According to Size-Hardness (SMASH) score was proposed to aid in preoperative planning by assessing stone size and hardness. This study aimed to evaluate the effectiveness of the SMASH score in selecting optimal candidates for RIRS in patients with stones smaller than 20 mm.

This retrospective observational study was conducted at the Pakistan Kidney and Liver Institute and Research Center (PKLI & RC) from September 2019 to September 2024. The study included patients aged over 14 years with renal stones between 1 cm and 2.5 cm undergoing their first RIRS procedure. Patients were excluded if they had infected urine, staghorn stones, stones larger than 2.5 cm, or required a second procedure. The SMASH score was calculated using Hounsfield units (HU) and stone size, and its utility in predicting successful stone clearance was assessed. Data on demographics, clinical characteristics, operative details, and postoperative outcomes were collected. Statistical analysis included Spearman’s correlation, logistic regression, and receiver operating characteristic (ROC) curve analysis.

The study analyzed 260 patients with a mean age of 44.88±15.25 years. Complete stone clearance was achieved in 80.4%, with higher success rates in patients with SMASH scores <15 (67.5%, p<0.001). Postoperative complications occurred in 12.7%, including urosepsis (9.2%) and UTIs (3.1%). Median operative and laser times were 80 minutes and 57.5 minutes, respectively, correlating positively with SMASH scores (ρ=0.194, ρ=0.185, p<0.01). Logistic regression identified stone size as a significant predictor of clearance (OR 5.479, p<0.001). The ROC curve analysis revealed a limited predictive ability of the SMASH score for stone clearance (AUC=0.306, p<0.001). Operative time increased with stone size (p<0.001), emphasizing preoperative complexity. The median hospital stay was one day, indicating rapid recovery.

The SMASH scores and stone size significantly influence the success of retrograde intrarenal surgery (RIRS). Lower SMASH scores and smaller stones correlate with higher clearance rates and fewer complications. The SMASH score demonstrated a weak predictive ability for stone clearance, stone size emerged as a strong predictor, emphasizing the need for preoperative planning.