Read the complete EBM Focus and earn CME.
Reference: N Engl J Med 2014 Sep 18;371(12):1100 (level 2 [mid-level] evidence)
Suspected nephrolithiasis is commonly encountered in the emergency department, with almost 1 million emergency department visits annually in the United States (J Urol 2014 Jan;191(1):90). Imaging is typically required to confirm the diagnosis. Noncontrast computed tomography (CT) is recommended to confirm a diagnosis of nephrolithiasis in adults by both the American Urological Association (AUA 2012 May PDF) and the European Association of Urology (EAU 2014 Mar PDF). Ultrasound has also been evaluated in this setting, and has several potential advantages over CT, including lack of radiation exposure and lower cost. A small diagnostic cohort study previously found that ultrasound had moderate sensitivity and high specificity for detecting nephrolithiasis in children (J Urol 2009 Oct;182(4 Suppl):1829). A new randomized trial in adults assessed initial diagnostic evaluation with ultrasound performed by an emergency physician, ultrasound performed by a radiologist, or abdominal CT in 2,759 patients presenting to the emergency department with suspected nephrolithiasis.
The study was powered to detect between-group differences of 5% for events with a prevalence of 10% or differences of 0.34% for events with a prevalence of 0.5%. All emergency physicians involved in the study had training and certification in bedside ultrasound, and subsequent imaging and management was left to the discretion of the treating physician. About 41% of patients in the bedside ultrasound group and 27% of those in the radiology ultrasound group had a subsequent CT as part of their initial workup. In contrast, about 5% of patients in the CT group had a subsequent ultrasound. There were no significant differences among groups in rate of return emergency department visits or hospitalizations after emergency department discharge; however, patients randomized to CT had significantly higher radiation exposure compared to other groups (see table below).
The findings from this new trial suggest bedside ultrasound and abdominal CT have similar rates of return emergency department visits and hospitalization after emergency department discharge. However, the large proportion of patients who were randomized to initial bedside ultrasound who subsequently received CT is a potential limitation, since some of the evaluation performance attributed to bedside ultrasound may have resulted from the combination of ultrasound and CT. Nonetheless, this new study demonstrates that bedside ultrasound may be a reasonable alternative to CT for assessing suspected nephrolithiasis in the emergency department, potentially reducing radiation exposure and costs associated with CT.
For more information see the Nephrolithiasis topic in DynaMed.