Clinical Question

What is the best initial imaging for a patient with suspected kidney stones?

Bottom Line

Initial point-of-care or radiology department ultrasonography is a safe and accurate approach to the patient with clinically suspected kidney stones, which helps reduce radiation exposure. Although computed tomography (CT) remains the most accurate test overall, a strategy beginning with ultrasonography (including point-of-care ultrasonography performed by an emergency physician) can help many patients avoid CT and its associated radiation. Note that these findings may not apply to patients who are very obese. (Level of Evidence = 1b–)

Synopsis

These researchers identified adults (range = 18 to 76 years of age) with flank or abdominal pain and clinical suspicion of kidney stones. Patients at risk of a serious alternate diagnosis, such as aneurysm or myocardial infarction, were excluded, as were men who weighed more than 129 kg (285 lb) and women who weighed more than 113 kg (250 lb). Patients were randomized into one of three groups: (1) point-of-care ultrasonography performed by trained emergency physicians, (2) ultrasonography performed in a radiology department, or (3) CT performed in the radiology department. Of the 3,638 patients originally assessed for eligibility, 2,776 were randomized, 2,759 were included in the intention-to-treat population, and approximately 4% were lost to follow-up. The groups were balanced regarding age, sex, race, pain, and other factors, but there is a puzzling discrepancy in group numbers: The CT group included 958 participants compared with 908 in the point-of-care ultrasonography group and 893 in the radiology department ultrasonography group. This leads me to question how well the allocation was concealed. The primary outcome was the likelihood of a complication due to a high-risk diagnosis, which occurred in less than 1% of patients in each group.

Not surprisingly, radiation exposure was significantly higher during the subsequent six months for those assigned to the CT group (17.2 vs. 9.3 to 10.1 mSv; P < .001). There were no significant differences between groups regarding rates of return to the emergency department, hospital admission after emergency department discharge, or self-reported pain score. The accuracy of the three strategies for the diagnosis of nephrolithiasis among those with at least 30 days of follow-up was remarkably similar, with sensitivities of 84% to 86% and specificities of 50% to 53%. Note that these numbers were based on the group that was initially randomized and included any subsequent imaging studies (usually CT), which occurred in 41% of the point-of-care ultrasonography group and in 27% of the radiology department ultrasonography group. Based on the initial imaging tests alone, the sensitivity was higher for CT (88% vs. 54% to 57%).

Study design: Randomized controlled trial (nonblinded)

Funding source: Government

Allocation: Uncertain

Setting: Emergency department

Reference: Smith-BindmanRAubinCBailitzJet alUltrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med2014; 371( 12): 1100– 1110.