Validating the MIMIC score as a predictor of successful spontaneous stone passage in patients managed conservatively for ureteric colic

Abstract

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%).