Outcomes and predictors of success after extracorporeal shock wave lithotripsy for renal stones: a retrospective study

OBJECTIVE: Extracorporeal shock wave lithotripsy (ESWL) is a first-line treatment for renal stones, yet outcomes are variable. This study aimed to identify predictors of stone clearance, complications, and number of treatment sessions in patients undergoing ESWL for kidney stones. PATIENTS AND METHODS: We conducted a retrospective cohort study at Aden Affiliated University Hospital (January 2017-May 2024) including 798 adults undergoing ESWL for renal stones. Primary outcome was stone clearance (< 4 mm residuals at three months). Secondary outcomes were complications and number of sessions. Univariate and multivariable logistic and Poisson regression were performed with Bonferroni correction. RESULTS: The cohort was predominantly male (99.6%) with median age 38 years (IQR 13). Median stone size was 9 mm (IQR 4) and density 1000 HU (IQR 450). Overall stone clearance was 86.8% (672 of 774 evaluable patients).. In univariate analysis, factors associated with clearance were lower BMI (OR 0.95 per kg/m², 95% CI 0.91-1.00, p = 0.05), smaller stone size (OR 0.94 per mm, 95% CI 0.88-1.00, p = 0.06), lower stone density (OR 0.98 per 100 HU, 95% CI 0.97-0.99, p < 0.001), and shorter skin-to-stone distance (OR 0.84 per mm, 95% CI 0.74-0.95, p 0.01). After multivariable adjustment, only stone density remained independently predictive (adjusted OR 0.98 per 100 HU, 95% CI 0.97-0.99, p < 0.001), and middle calyx location predicted better clearance than lower calyx (adjusted OR 2.70, 95% CI 1.09-6.68, p = 0.03). Complications occurred in 14 patients (1.8%) and were associated with low pain tolerance (OR 16.74, 95% CI 4.09-68.54, p < 0.001) and anticoagulation (OR 59.31, 95% CI 3.53-997.2, p = 0.004). Median sessions was 1 (range 1-4); higher number of sessions correlated univariately with power level (ρ = 0.191, p < 0.001), size (ρ = 0.144, p < 0.001), and density (ρ = 0.124, p < 0.001), but none remained significant at multivariable assessment. CONCLUSIONS: Stone density is the strongest independent predictor of ESWL success, with higher density associated with significantly lower clearance. Middle calyx stones have better outcomes than lower calyx. Complications are rare but more frequent with low pain tolerance and anticoagulation. These findings guide patient selection and counseling.