Ultrasound vs. CT as Initial Test for Kidney Stones

For patients with suspected nephrolithiasis, clinical outcomes are similar when ultrasonography or computed tomography (CT) is used as the initial imaging test, according to a “real-world” trial published in the New England Journal of Medicine.

The pragmatic comparative effectiveness study included 2759 patients with suspected nephrolithiasis, seen at 15 diverse academic emergency departments. Patients were randomly assigned to initial evaluation with point-of-care ultrasonography, performed by an emergency physician; radiology ultrasonography, performed by a radiologist; or abdominal CT. All other clinical decisions, including orders for additional imaging tests, were made by the treating physician.

At 30 days, the rates of high-risk diagnoses with complications potentially related to missed or delayed diagnosis were compared between groups. Other outcomes of interest included 6-month cumulative radiation exposure and adverse events. At least one follow-up visit was available for 2646 patients.

Just 11 patients had high-risk diagnoses with complications within 30 days: a rate of 0.4 percent, with no significant difference by initial imaging test. In five of these patients, the final diagnosis was pyelonephritis, urosepsis, and bacteremia. Both ultrasound groups had lower 6-month cumulative radiation exposure compared with the CT group.

The rates of serious adverse events were similar among groups: between 11 and 12 percent. Just 0.4 percent of patients had serious adverse events related to study participation. The pain scores and rates of return emergency visits or hospitalization were similar between groups. Diagnostic accuracy was 34.5 percent with point-of-care ultrasonography, 31.2 percent with radiology ultrasonography, and 32.7 percent with CT.

Abdominal CT has high sensitivity in the evaluation of suspected kidney stones. However, it has drawbacks, including high costs, radiation exposure, and a high rate of incidental findings.

Ultrasonography is a good alternative for evaluation of suspected nephrolithiasis in everyday clinical practice, the new trial suggests. Although it cannot match the sensitivity of CT, it offers comparable accuracy, with lower cumulative radiation exposure and no increase in high-risk diagnoses with complications. The authors believe that an initial ultrasound strategy can avoid the need for CT in most patients [Smith-Bindman R, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med 2014; 371:1100–1110].