Ultrasound may be as effective as CT in diagnosing kidney stones

Ultrasound may be an effective way to diagnose kidney stones with less radiation exposure, a study found.

Ultrasound may be an effective way to diagnose kidney stones with less radiation exposure, a study found.

The study included 2,759 patients who presented with suspected cases of kidney stone to 15 geographically diverse academic hospital EDs, 4 of which were “safety net” hospitals. Patients were randomized to 1 of 3 groups: point-of-care ultrasonography performed by an emergency physician, ultrasonography performed by a radiologist, or abdominal CT. Primary outcomes included high-risk diagnoses with complications that could be related to missed or delayed diagnoses and cumulative radiation exposure from imaging. The study, funded by the Agency for Healthcare Research and Quality, appeared in the Sept. 18 New England Journal of Medicine.

The study found a 0.4% rate (11 patients) of high-risk diagnoses with complications within 30 days, and this did not vary significantly by imaging method: 6 patients (0.7%) with ED ultrasonography, 3 (0.3%) with radiology ultrasonography, and 2 (0.2%) with CT (P=0.30). High-risk diagnoses included abdominal aortic aneurysm with rupture, pneumonia with sepsis, appendicitis with rupture, diverticulitis with abscess or sepsis, bowel ischemia or perforation, renal infarction, renal stone with abscess, pyelonephritis with urosepsis or bacteremia, ovarian torsion with necrosis, or aortic dissection with ischemia.

The mean 6-month cumulative radiation exposure was significantly lower in the ultrasonography groups than in the CT group (10.1 mSv and 9.3 mSv vs. 17.2 mSv; P<0.001). The radiation in the ultrasound groups resulted from some patients going on to have additional testing, some of which included CTs. Median length of stay in the ED was significantly longer in the radiology ultrasound group: 7.0 hours compared to 6.3 hours in the ED ultrasound group and 6.4 hours in the CT group (P<0.001 for radiology versus each of the other 1 groups). Return ED visits, hospitalizations, and diagnostic accuracy did not differ significantly among the groups. Based on the result of the first imaging test patients underwent, ultrasonography had lower sensitivity and higher specificity than CT. Sensitivity was 54% for point-of-care ultrasonography, 57% for radiology ultrasonography, and 88% for CT (P<0.001), and specificity was 71%, 73%, and 58%, respectively (P<0.001). There was no significant difference in results between those with and those without complete follow-up.

The authors emphasized the results do not suggest that patients 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. They noted that the emergency physicians in the study were all trained and certified in the use of point-of-care ultrasound, which might not be true in all facilities.

An editorialist agreed that the authors' conclusion seemed like a reasonable course, and while CT had higher sensitivity than ultrasonography, the increased sensitivity did not lead to better clinical outcomes. He added, “Regardless of which imaging method is used, providers should remember to tell their patients that new stone formation can be prevented and to give them preventive strategies that should reduce the number of future emergency department visits for renal colic.”