Ultrasonography is known to be less sensitive than computed tomography for diagnosing kidney stones. But the initial use of ultrasonography, followed by CT imaging if indicated, results in less cumulative radiation exposure for patients without increasing the risk of adverse clinical outcomes or missed diagnoses, according to findings published online Sept 18 in the New England Journal of Medicine (doi:10.1056/NEJMoa1404446).
The multicenter study, led by Dr. Rebecca Smith-Bindman of the University of California, San Francisco, and colleagues, randomized 2,759 patients presenting in hospital emergency departments with symptoms of nephrolithiasis to receive initial ultrasonography performed by an emergency physician (n = 908); ultrasonography performed by a radiologist (n = 893), or abdominal CT (n = 958), with all further diagnostic and management decisions left up to the physician.
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Ultrasonography as the initial diagnostic test for kidney stones can reduce overall radiation exposure.
High-risk diagnoses with complications within 30 days of initial imaging occurred infrequently across the groups (0.4% for all three, n = 11), with no significant differences seen among the groups (P = .30). Within 6 months, serious adverse advents occurred in 12.4% of patients assigned initial ED ultrasonography, 10.8% in those assigned radiology ultrasonography, and 11.2% of those assigned to CT (P = .50) with no significant differences in pain scores, return emergency department visits, or hospitalizations. Cumulative radiation exposure at 6 months, however, was significantly higher for the CT arm than for the two ultrasonography arms (P < .001).
Dr. Smith-Bindman and colleagues emphasized in their analysis that their results do not imply that patients with suspected nephrolithiasis should undergo only ultrasound imaging, “but rather that ultrasonography should be used as the initial diagnostic imaging test, with further imaging studies performed at the discretion of the physician on the basis of clinical judgment.” Patients with nephrolithiasis often undergo repeat imaging over time, the researchers observed, and “replacing initial CT with ultrasonography for this often-recurring disease reduced overall radiation exposure.”
Dr. Smith-Bindman and colleagues noted as a limitation of their study the fact that treatment assignment could not be blinded. The study was funded by the Agency for Healthcare Research and Quality; none of its authors declared financial conflicts of interest.