Risk Factors of Asymptomatic Kidney Stone Passage in Adults with Recurrent Kidney Stones.

Background Kidney stones are a common health problem and are characterized by a high risk of recurrence. A certain number of kidney stones pass asymptomatically. Data regarding the frequency of asymptomatic spontaneous stone passages are limited. Methods To assess the frequency of asymptomatic spontaneous stone passage and its covariates, we conducted a post hoc analysis of the prospective randomized NOSTONE trial. All asymptomatic spontaneous stone passages were identified by comparing the total number of kidney stones on low-dose noncontrast computed tomography (CT) imaging at the beginning and end of the study, considering symptomatic stone passages and surgical stone removal. The statistical analysis focused on the association of independent variables and the number of asymptomatic spontaneous stone passages using linear regression analyses. Results Of the 416 randomized patients, 383 with both baseline and end-of-study CT were included in this analysis. The median follow-up period was 35 months, the median patient age was 49 years (interquartile range [IQR], 40-55), and 20% of the patients were female. A total of 442 stone events occurred in 209 of 383 (55%) patients: 217 of 442 (49%) were symptomatic spontaneous stone passages, 67 of 442 (15%) were surgically removed stones, and 158 of 442 (36%) were asymptomatic spontaneous stone passages. The median size of asymptomatic stones (2.4 mm; IQR, 1.95-3.4) and the size of symptomatic stones (2.15 mm; IQR, 1.68-2.79) that passed spontaneously were not significantly different (P = 0.37). The number of asymptomatic spontaneous stone passages was significantly associated with a higher number of stones on CT at randomization (P = 0.001). Limitations include the lack of data on stone size at the time of passage and overrepresentation of White men. Conclusions Asymptomatic stone passage was common in patients with recurrent calcium-containing kidney stones. The higher the number of stones at presentation, the more likely it was that a kidney stone would spontaneously pass over time without causing any symptoms.