Time to stone passage for observed ureteral calculi: A guide for patient education

Purpose: We analyze the natural history of stone passage in patients with ureterolithiasis, and define factors predictive of spontaneous passage. Materials and Methods: A total of 75 patients with ureteral calculi were prospectively followed for stone passage. Clinical data included patient gender and age, stone size and location, pain medication requirements and interval to stone passage. Of the 75 patients 13 (17%) required intervention and 62 (83%) were followed until spontaneous stone passage. Stones requiring intervention were not included in the time to passage analysis. Results: Of the 75 patients 41 (55%) had ureteral stones 2 mm. or smaller with an average time to stone passage of 8.2 days and only 2 (4.8%) required intervention, 18 (24%) had stones between 2 and 4 mm. with an average time to stone passage of 12.2 days and 3 (17%) required intervention, and 16 had stones 4 mm. or greater with an average time to stone passage of 22.1 days and 8 required intervention. For 95% of stones to pass it took 31 days for those 2 mm. or less, 40 days for those 2 to 4 mm. and 39 days for those 4 to 6 mm. Multivariate analysis revealed that size, location and side were statistically related to stone passage interval (p = 0.012). Stones that were smaller, more distal and on the right side were more likely to pass spontaneously and required fewer interventions. Conclusions: Interval to stone passage is highly variable and dependent on stone size, location and side. Degree of pain, and patient gender and age had no bearing on the time to stone passage. Of ureteral stones 95% 2 to 4 mm. pass spontaneously but passage may take as long as 40 days. Intervention may be required in 50% of ureteral calculi greater than 5 mm.