Ultrasound Matches CT for Kidney Stone Imaging
May 17, 2014
ORLANDO, Florida — Ultrasound was comparable to CT in its ability to discriminate between renal calculi and other causes of flank pain, according to the results of a new study.
"Routine utilization of CT as a knee-jerk response for someone presenting with acute colic is inappropriate, not only for cost but for radiation exposure," said Marshall L. Stoller, MD, professor and vice chair of urology at the University of California, San Francisco.
More important, this study shows that using ultrasound has no adverse impact on patient outcomes, said Dr. Stoller.
The results of the study were presented here at the American Urological Association 2014 Annual Scientific Meeting.
A Multicenter Study
Dr. Stoller and colleagues at 15 academic medical centers conducted a randomized trial in which adult patients presenting to an emergency department with suspected nephrolithiasis were randomly assigned to receive point-of-care ultrasound performed by an emergency physician, ultrasound performed by a radiologist, or abdominal CT. Additional tests were at the discretion of each patient's physician.
The investigators looked at the incidence of serious adverse events diagnosed within 30 days of imaging, cumulative radiation exposure, and cost. Follow-up with detailed, structured patient interviews was done at 3 and 7 days, and again at 1, 3, and 6 months.
The incidence of serious adverse events among patients assigned to CT was 11.1%, compared with 12.3% for patients who underwent ultrasound performed by an emergency physician and 10.6% for those whose ultrasound scans were performed by a radiologist. The differences were not significant.
Severe adverse events — including abdominal aortic aneurysm with rupture, pneumonia with sepsis, appendicitis with rupture, inflammatory bowel conditions and renal infarction, pyelonephritis with urosepsis, and ovarian torsion with necrosis — occurred in 5 of 908 patients (0.55%) assigned to emergency-physician-performed ultrasound, 3 of 893 patients (0.34%) assigned to radiologist-performed ultrasound, and 4 of 958 patients (0.42%) assigned to CT.
Not surprisingly, patients who underwent ultrasound had significantly lower average cumulative radiation exposures, at 10.5 mSv and 9.3 mSv for emergency-physician- and radiologist-performed ultrasound, respectively, compared with 17 mSv for patients who underwent CT (P < .0001).
There were no significant differences in hospital readmissions after discharge, average pain scores, pain resolution, or subsequent serious adverse events, the investigators found.
Average imaging costs were about 33% to 50% higher for CT (average, $300) than for ultrasound ($150 if done by an emergency physician, and $200 if done by a radiologist).
Concerns About Radiation
This study shows that emergency department physicians need not fear missing a diagnosis of kidney stones or other causes of acute pain if they choose ultrasound over CT as an initial imaging modality, said Margaret Pearle, MD, PhD, professor of urology at the University of Texas Southwestern Medical Center at Dallas and the Center for Mineral Metabolism and Clinical Research.
And patients can be confident that their chance of getting an accurate diagnosis is comparable, she added.
"I think in our institution, probably like the majority of institutions, if someone comes in with acute flank pain, the first test is a CT, although we're starting to see a little bit of a trend toward ultrasound," Dr. Pearle told Medscape Medical News.
The shift appears to be driven more by patient and clinician concerns about radiation exposure, rather than administrative worries over cost, she said.
"There's tremendous fear right now, particularly on the part of patients. They hear that radiation exposure is bad, and they don't [want to be exposed]," she said. "Stone disease is one of those conditions that is associated with repeated imaging studies because of repeated symptomatic episodes."
Dr. Pearle was not involved in the study.
Because of fragmentation and lack of coordination of healthcare, some patients get repeat exposure to ionizing radiation for the same episode of pain, said Dr. Stoller.
"It is not uncommon in my clinic that you'll see someone in their 20s coming in with 5 or 6 CTs from the past week or 2. That's a huge amount of radiation," he said.
The study was supported by the National Institutes of Health. Dr. Stoller and Dr. Pearle have reported no relevant financial relationships.
American Urological Association (AUA) 2014 Annual Scientific Meeting. Abstract PD4-03. Presented May 16, 2014.