Few risks seen with initial ultrasonography in nephrolithiasis

Key clinical point: Ultrasonography may be preferable to computed tomography in initial imaging to diagnose kidney stones.

Major finding: Initial ultrasound, followed by CT if indicated, did not increase incidence of high-risk diagnoses with complications or adverse outcomes compared with initial CT; patients also saw lower cumulative radiation compared with initial CT.

Data source: Study of 2,759 patients with suspected nephrolithiasis enrolled from 15 U.S. hospital emergency departments between October 2011 and February 2013, randomized to initial screening with CT or ultrasonography, and followed up for 6 months.

Disclosures: None of the study authors declared financial conflicts of interest.

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Start with ultrasonography and then proceed to CT

On the basis of the study findings, it is reasonable for a physician to use ultrasonography as the initial imaging method for a patient presenting to the emergency department with suspected nephrolithiasis, remembering that additional imaging studies should be used when clinically indicated. Although CT had higher sensitivity than ultrasonography, this increased sensitivity did not lead to better clinical outcomes.

It should be emphasized that ultrasonography when used alone is not very sensitive for detecting stones. However, the approach of starting with ultrasonography and then proceeding to CT if indicated resulted in similar levels of sensitivity in the three groups. It is reassuring that high-risk diagnoses were rarely missed with this approach.

Dr. Gary Curhan is with Brigham and Women’s Hospital and Harvard Medical School, Boston. Dr. Curhan disclosed financial ties with AstraZeneca, Exponent, UpToDate, Allena, the American Society of Nephrology, and the American Urological Association.




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.

Ultrasonography as the initial diagnostic test for kidney stones can reduce overall radiation exposure. ©decade3d/

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.

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