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Computed tomography (CT) is the most common imaging modality used for diagnosing nephrolithiasis, but it exposes patients to ionizing radiation; ultrasound may be an appropriate alternative (NEJM JW Emerg Med Jul 9 2010,NEJM JW Emerg Med May 23 2014). Researchers at 15 U.S. emergency departments (EDs) compared outcomes in 2759 patients with suspected nephrolithiasis who were randomized to CT, ultrasound performed by radiologists, or bedside ultrasound performed by trained emergency physicians as the initial imaging study. Subsequent tests and treatments, including additional imaging tests, were performed at the discretion of treating physicians.
In intention-to-treat analysis (4% of patients were lost to follow-up), mean 6-month radiation exposures were significantly lower in the two ultrasound groups than in the CT group. Rates of serious adverse events were similar in all three groups, as were ED readmissions and average pain scores. Although 41% of the bedside-ultrasound group and 27% of the radiology-ultrasound group underwent subsequent CT imaging in the ED, overall ED costs remained lower for patients who received ultrasound first.
Smith-Bindman R et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med 2014 Sep 18; 371:1100. (http://dx.doi.org/10.1056/NEJMoa1404446)
Comment
Not all patients who present with renal colic need imaging (NEJM JW Emerg Med Apr 17 2014). However, if imaging is needed, the strategy of performing ultrasound first — either by an emergency physician or a radiologist — is the right one. Of note, a strength of this study — its pragmatic nature, allowing physician discretion in follow-up testing — is also a limitation: We don't know what formal or informal criteria these physicians used in deciding when to perform CT after ultrasound imaging.