Predicting ureteral stones in emergency department patients with flank pain: an external validation of the STONE score.

Abstract

The ability to objectively predict which emergency department patients are likely to have a ureteral stone may aid in cost-effectiveness and patient-centered diagnostic imaging decisions. We performed an external validation of the STONE score, a clinical prediction rule for the presence of uncomplicated ureteral stones in emergency department patients developed at Yale University School of Medicine. Five hundred thirty-six (536) consecutive patients evaluated in an urban tertiary care emergency department for the possible diagnosis of ureteral stone were retrospectively reviewed. The STONE score uses five factors (gender, duration of pain, race, nausea/vomiting, erythrocytes on urine dipstick) to categorize patients into low, medium, and high probability of having a ureteral stone. The total STONE score risk is 0-13 and divided into three groups: low risk=0-5, moderate risk=6-9, and high risk=10-13. Of the 536 patients evaluated for suspected ureteral stone, 257 (47.8%) had a ureteral stone. Mean patient age was 45.9years (SD 16.3), and gender distribution was 43.9% female and 56.1% male. Distribution of STONE score risk was 24.1% low, 48.1% moderate, and 27.7% high. Diagnosis of ureteral stone by STONE score risk was 14% for low-risk group, 48.3% for moderate-risk group, and 75.8% for high-risk group. This distribution is consistent with internal validation at Yale University School of Medicine, where values were 8.3-9.2% for low risk, 51.3-51.6% for moderate risk, and 88.6-89.6% for high risk. Our study validates the use of the STONE clinical score to categorize patients as low, moderate, and high risk for ureteral stone. This could help guide development of clinical decision rules for diagnostic studies and imaging in the future.