Sensitivity of Emergency Bedside Ultrasound to Detect Hydronephrosis in Patients with Computed Tomography-proven Stones

Introduction: Non-contrast computed tomography (CT) is widely regarded as the gold standard for diagnosis of urolithiasis in emergency department (ED) patients. However, it is costly, time-consuming and exposes patients to significant doses of ionizing radiation. Hydronephrosis on bedside ultrasound is a sign of a ureteral stone, and has a reported sensitivity of 72-83% for identification of unilateral hydronephrosis when compared to CT. The purpose of this study was to evaluate trends in sensitivity related to stone size and number. Methods: This was a structured, explicit, retrospective chart review. Two blinded investigators used reviewed charts of all adult patients over a 6-month period with a final diagnosis of renal colic. Of these charts, those with CT evidence of renal calculus by attending radiologist read were examined for results of bedside ultrasound performed by an emergency physician. We included only those patient encounters with both CT-proven renal calculi and documented bedside ultrasound results. Results: 125 patients met inclusion criteria. The overall sensitivity of ultrasound for detection of hydronephrosis was 78.4% [95% confidence interval (CI)= 70.2-85.3%]. The overall sensitivity of a positive ultrasound finding of either hydronephrosis or visualized stones was 82.4% [ 95% CI: 75.6%, 89.2%]. Based on a prior assumption that ultrasound would detect hydronephrosis more often in patients with larger stones, we found a statistically significant (p= 0.016) difference in detecting hydronephrosis in patients with a stone = 6 mm (sensitivity=90% [95% CI=82-98%]) compared to a stone < 6 mm (sensitivity=75% [95% CI=65-86%]). For those with 3 or more stones, sensitivity was 100% [95% CI=63-100%]. There were no patients with stones =6 mm that had both a negative ultrasound and lack of hematuria. Conclusion: In a population with CT- proven urolithiasis, ED bedside ultrasonography had similar overall sensitivity to previous reports but showed better sensitivity with increasing stone size and number. We identified 100% of patients with stones >= 6 mm that would benefit from medical expulsive therapy by either the presence of hematuria or abnormal ultrasound findings.