External Validation of the STONE Score, a Clinical Prediction Rule for Ureteral Stone: An Observational Multi-institutional Study.

Study objective The STONE scoreis a clinical decision rule that classifies patients with suspectednephrolithiasis into low-, moderate-, and high- scoregroups, with corresponding probabilities of ureteralstone. We evaluate the STONE scorein a multi-institutional cohort compared with physician gestalt and hypothesize that it has a sufficiently high specificity to allow clinicians to defer computed tomography (CT) scan in patients with suspectednephrolithiasis. Methods We assessed the STONE scorewith data from a randomized trial for participants with suspectednephrolithiasis who enrolled at 9 emergency departments between October 2011 and February 2013. In accordance with STONE predictors, we categorized participants into low-, moderate-, or high- scoregroups. We determined the performance of the STONE scoreand physician gestalt for ureteralstone. Results Eight hundred forty-five participants were included for analysis; 331 (39%) had a ureteralstone. The global performance of the STONE scorewas superior to physician gestalt (area under the receiver operating characteristic curve=0.78 [95% confidence interval {CI} 0.74 to 0.81] versus 0.68 [95% CI 0.64 to 0.71]). The prevalence of ureteralstone on CT scan ranged from 14% (95% CI 9% to 19%) to 73% (95% CI 67% to 78%) in the low-, moderate-, and high- scoregroups. The sensitivity and specificity of a high scorewere 53% (95% CI 48% to 59%) and 87% (95% CI 84% to 90%), respectively. Conclusion The STONE scorecan successfully aggregate patients into low-, medium-, and high-risk groups and predicts ureteralstone with a higher specificity than physician gestalt. However, in its present form, the STONE scorelacks sufficient accuracy to allow clinicians to defer CT scan for suspected ureteralstone.