Predictors of stone related events in asymptomatic untreated intra-renal calculi.

Purpose There is a lack of data on the natural history of asymptomatic intra-renal calculi. In this study we investigate stone related events (SREs) in patients with untreated intra-renal calculi. We also investigate predictive factors for SREs. Materials and Methods All patients diagnosed with an asymptomatic intra-renal calculus on CT KUB managed conservatively with interval imaging for ≥6 months were included. Patients were evaluated for any stone related event. The rate of event according to calculus size, location and number of calculi was also analysed. Multivariate logistic regression analysis was performed to determine significant predictors for SREs. Results In total, 266 renal units from 177 patients met inclusion criteria. The mean stone size was 4.44mm (range of 1-25mm). Duration of follow-up was 43.78 ± 26.86 months (range 6-106 months). The overall rate of SRE's including intervention (n=80) and spontaneous stone passage following ureteric colic (n= 40) was 45.1% (n=120/266). Stones >5mm were more likely to lead to an event compared to stones ≤5mm (OR: 2.94; p=0.01). Inter-polar stones and stones located in multiple calyces were more likely to cause a SRE than lower pole stones (OR: 2.05; p=0.05 and OR:2.29; p=0.03 respectively). Conclusion In this large series of patients with asymptomatic intra-renal calculi, the incidence of a spontaneous SRE was 45.1% after 41 months. Stone size and stone location were significant predictors for stone related event. Information from this study will enable urologists to accurately risk stratify patients with asymptomatic renal stones.