RSNA: CT use in the ED on exponential growth path
CHICAGO—If the current growth trend in CT use in the emergency department (ED) continues, by 2011, nearly 20 percent of all ED visits may involve a CT exam, according to results of a study presented Nov. 29 at the annual meeting of the Radiological Society of North America (RSNA) and published online in Radiology.

“It’s not surprising that CT utilization has increased,” said lead author David B. Larson, MD, MBA, director of quality improvement in the department of radiology at Cincinnati Children’s Hospital Medical Center in Ohio. “What’s surprising is the sustained high rate of that growth.”

Larson and colleagues collected data from the National Hospital Ambulatory Medical Care Survey (NHAMCS) from 1995 through 2007 to identify nationwide trends associated with CT use in the ED. The researchers analyzed a mean of 30,044 ED visits from each year to estimate overall usage of CT in the ED.

The researchers found that from 1995 to 2007 the number of ED visits that included a CT exam increased from 2.7 million to 16.2 million, constituting a 5.9-fold increase and a compound annual growth rate of 16 percent. In contrast, other reports peg compound annual growth rate in CT use at 10.4 percent in inpatient and outpatient settings. The percentage of ED visits involving a CT exam rose from 2.8 percent in 1995 to 13.9 percent in 2007.

The growth rate had not started to taper by 2007. “[I]t is impossible to predict when or at what level the overall use of CT in the ED will begin to level off,” according to Larson and colleagues.

The researchers noted that the total population radiation dose increased at a higher rate than the number of visits involving CT. They projected a 23-fold increase in population radiation dose from 1995 to 2007. That’s because ED visits often involve multiple CT exams and higher dose exams are increasing at a faster rate than lower dose studies.

Larson and colleagues evaluated data by patient and hospital characteristics and chief complaints associated with CT use. They reported that CT use in the ED was greater in older patients than in younger ones. The level of CT use had not reached an inflection point, where growth begins to decelerate, in 2007 in any age group except patients younger than 18 years, which reached an inflection point between 2005 and 2006.

Other subgroups with significantly higher CT imaging rates included white patients versus black patients and those admitted to the hospital or transferred to another facility. The percentage of visits involving CT tended to be slightly higher among patients with private insurance and or Medicare or Medicaid coverage than among those in the self-pay or no charge groups, according to the authors.

The researchers also found that CT use was significantly higher in metropolitan regions than in non-metropolitan regions.

Chief complaints changed over the course of the study.

In the first half of the study, the most common chief complaint was headache, which was replaced by abdominal pain in the second half of the study. Although not commonly linked with CT in the first half of the study, chest and side or flank pain were among the most common chief complaints in the latter years.

Data in perspective

“[R]ecent developments, such as increased awareness of cost, radiation concerns, national healthcare reform legislation and the economic recession are likely to inhibit further growth,” Larson predicted. He identified cost containment programs, interventions to improve adherence to evidence-based guidelines and concerns regarding radiation exposure as factors that might limit the growth in CT use and pointed out the computerized physician order entry with decision support has decreased the frequency of low-yield imaging in the outpatient setting.

The researchers acknowledged several limitations to the study. Specifically, NHAMCS does not address possible external causes of increased CT use such as increasing acuity of patients in the ED or clinical referrals to the ED specifically for CT. The study team did not recommend that the growth models be used to forecast future use of CT as recent developments are likely to affect growth.

“Our emphasis now should be on carefully evaluating the use of CT in specific situations and making sure it is used appropriately,” he concluded. The authors also suggested, “Our findings highlight the fact that some examinations account for greater increases in population radiation dose than do others and may warrant higher priority for dose reduction efforts.”