Initial US for suspected nephrolithiasis cuts radiation dose

Using ultrasound (US) instead of CT as the initial imaging method for suspected nephrolithiasis can spare some patients from radiation while not significantly affecting outcomes, according to a study published in the September issue of the New England Journal of Medicine.

The study also found that patients who had an initial US instead of a CT had no significant differences in high-risk diagnoses with complications, serious adverse events, pain scores, return emergency department visits, or hospitalizations.

Even though CT carries a cancer risk from radiation, it is the most common initial imaging test for suspected nephrolithiasis because of its high sensitivity, noted the authors.

However, no evidence has shown that increased CT use, despite its higher sensitivity, improves patient outcomes, commented lead researcher R. Smith-Bindman, MD, of the University of California in San Francisco, and colleagues.

“There is a lack of consensus about whether the initial imaging method for patients with suspected nephrolithiasis should be [CT] or ultrasonography,” they wrote.

The multi-center, randomized study of 2,759 patients compared the initial use of US with CT by assessing the patient outcomes. Study patients were recruited in 15 geographically diverse academic emergency departments, four of which were safety-net hospitals, from October 2011 through February 2013. The patients were then randomly assigned: 908 to point-of-care ultrasonography, 893 to radiology ultrasonography, and 958 to CT.

The incidence of high-risk diagnoses with complications in the first 30 days was low and did not vary according to imaging method. The mean six-month cumulative radiation exposure was significantly lower in the US groups than in the CT group, the authors said.

Related adverse events were infrequent and similar across all groups. Return emergency department visits, hospitalizations, and diagnostic accuracy did not differ significantly among the groups, the authors said.

“Our results do not suggest that patients 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,” the authors wrote.

Although more patients in the study’s US groups underwent additional imaging, the majority of patients in the US groups did not undergo CT. The radiation exposure for US groups was more than zero because some patients ultimately underwent CT. However, despite additional CT imaging, the mean radiation exposure in the US groups was about half that in the CT group, they noted.