BACKGROUNDS: The MIMIC score was designed to predict the likelihood of spontaneous stone passage (SSP) in patients presenting with ureteric colic and given a trial of conservative management. The objective of this study was to determine the external validity of the MIMIC score. METHODS: Cross-sectional, retrospective cohort study that reviewed patients over a 2-year period presenting with ureteric colic who were given a trial of conservative management. Patient-factors were recorded, and their MIMIC score calculated and compared to the observed outcome. Discrimination was determined using an area under the receiver-operating curve with an AUC >
0.7 considered validated and calibration using calibration plot. RESULTS: Three hundred ninety-nine patients were included. The median age was 49 (IQR 37-60). 79% were males. The mean stone size for successful SSP was 3.8 mm compared to 4.8 mm for failed SSP. 88% of stones passed spontaneously. The AUC was 0.68 (95% CI: 0.60-0.77). The calibration plot showed an underestimation of SSP. In the lowest quintile of patients with a mean predicted SSP rate of 46%, the observed SSP rate was 74% (95% CI: 63-83%). With a higher predicted SSP rate, the MIMIC score was accurate. In the highest quintile of patients with a mean predicted SSP rate of 90%, the observed SSP rate was 92% (95% CI: 84-97%). CONCLUSION: In this population, the prediction of the MIMIC score were not sufficiently accurate. There was overall an underestimation of SSP. The MIMIC score was accurate for patients who had a higher likelihood of SSP (>
83%).