Patient- and visit-level factors, as opposed to physician-level factors, are the predominant predictors of whether an imaging exam is ordered during an emergency department (ED) visit, according to a study published online June 25 in Radiology.

ED physicians’ level of experience, residency training, annual workload and sex all failed to correlate with imaging use after a hierarchical logistic regression of possible imaging predictors, explained Hannah J. Wong, PhD, of York University, Toronto, and colleagues.

Conclusions were based on an analysis of 88,851 ED visits at Massachusetts General Hospital (MGH) in Boston, in 2011. During the study period, imaging utilization in the ED was 45.4 percent, compared with the 2010 national average of 47.2 percent.

A number of patient and visit factors were found to impact the likelihood of imaging during the ED visit, including prior ED visits, referral source to the ED, method of arrival and clinical reason for the visit, according to Wong and colleagues. A busy ED, another visit-level factor, was found to lead to more high-cost imaging, while less busy EDs increased the odds of low-cost imaging 11 percent.

“We speculated that low-cost imaging may be performed more often when the ED is least busy because ED physicians would have more time to order and review the examinations during a comprehensive assessment,” wrote the authors, adding that ordering high-cost imaging early in the workup may free up more of the ED physician’s time in the short term, despite the fact that use of advanced imaging results in longer patients stays—and increased costs—overall.

The unadjusted variation between physicians, measured as intraclass correlation coefficient (ICC), was 12.66 percent for low-cost imaging and 23.63 percent for high-cost imaging. However, after adjusting for patient- and visit-level characteristics, variation in imaging use attributable to the practice style of the physician was 0.97 percent for low-cost imaging and 1.07 percent for high-cost imaging across the ED as a whole.

Four of the 46 ED physicians involved in the study would be considered high outliers for the use of imaging in their patients, but Wong and colleagues said the impact of other factors on utilization means focusing on physician-specific rates of ED imaging could lead to misclassification and limited results for utilization reduction efforts.

“Discussion of quality and cost-control efforts is promoted by reporting interphysician variation for use of ED imaging in this manner,” they wrote. “However, we would urge caution in the use of such metrics to remediate outlier physicians because only about 1 percent (measured by ICC) of overall variation in ED imaging use is directly affected by physicians.”