Ultrasound as effective as CT in diagnosing kidney stones without added radiation risk: AHRQ-funded study

Press Release Date: September 17, 2014

Broader use of ultrasound in diagnosing kidney stones may be effective and result in less exposure to potentially harmful radiation, according to a study published today in the New England Journal of Medicine. The findings come from a study funded by the Agency for Healthcare Research and Quality (AHRQ), to investigate whether ultrasound would be a suitable alternative to CT.

"Our results do not suggest that patients should 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 on the basis of clinical judgment," said lead author Rebecca Smith-Bindman, M.D., professor of radiology at the University of California-San Francisco. 

Abdominal CT scan has become the most common initial imaging test for suspected cases of kidney stones. It is highly accurate in diagnosing kidney stones and can be performed in most hospital radiology or emergency departments (EDs). However, CT exposes patients to potentially harmful radiation doses, can reveal findings that lead to unnecessary care, and is more costly to perform. Ultrasound does not expose patients to radiation, can be performed in the ED or radiology department, and is less expensive than CT.

In this randomized controlled trial, researchers assigned 2,759 patients who came to hospital EDs with suspected cases of kidney stones into one of three groups: initial diagnostic testing by point-of-care ultrasound (in the ED), radiology ultrasound, or abdominal CT scan.

After 30 days, researchers found no significant differences among the three groups in the rate of high-risk diagnoses of kidney stones with complications that could have been related to missed or delayed diagnoses. After six months, researchers found that the proportion of patients with confirmed diagnoses of kidney stones was similar for all three study groups, but patients who initially received a CT scan had significantly higher radiation exposure than patients in the two ultrasound groups. Cumulative radiation exposure is associated with an increased risk of cancer. 

Some patients in the ultrasound groups went on to have additional testing, some of which included CTs. This resulted in an average radiation exposure of about half that of the CT group.

Researchers found no significant differences among the three groups in the rates of serious adverse events, pain, return trips to the ED, or hospitalizations.

Pain associated with the development of kidney stones is a common reason for ED visits. It accounted for more than 1.3 million ED visits in 2009, an average of 3,600 ED visits per day, according to 2012 data from AHRQ's Healthcare Cost and Utilization Project. Patients with kidney stones frequently undergo repeated imaging over time.

"We know that many patients experience kidney stones more than once," said AHRQ Director Richard Kronick, Ph.D. "The data show, in fact, the likelihood of re-occurrence to be as high as 50 percent within five years of the first event. Given this frequency, the study findings can help clinicians make the best possible decisions about how to effectively diagnose kidney stones while reducing the risk for patients from potential cumulative radiation exposures." 

The study was conducted in 15 geographically diverse academic hospital EDs, four of which were "safety-net" hospitals that serve largely low-income communities. Patients ranged in age from 18 to 76, and their care during the ED visit was managed by the treating physician, including decisions about further imaging.

The article, "Ultrasonography versus Computed Tomography for Suspected Nephrolithiasis," was funded by a grant from AHRQ. A research agency within the U.S. Department of Health and Human Services, AHRQ is the lead federal agency charged with producing evidence to make health care safer, higher quality, more accessible, equitable and affordable, and to work with HHS and other partners to make sure that the evidence is understood and used. For more information, visit www.ahrq.gov.

For more information, please contact AHRQ Public Affairs: (301) 427-1244.

Page last reviewed September 2014
Internet Citation: Ultrasound as effective as CT in diagnosing kidney stones without added radiation risk: AHRQ-funded study. Content last reviewed September 2014. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/news/newsroom/press-releases/2014/kidney_stones.html