The Impact of Risk Standardization on Variation in CT Use and Emergency Physician Profiling

The purpose of this study is to use detailed electronic health record data to profile the use of condition-specific, risk-standardized imaging by emergency physicians.

CT utilization in four emergency departments in a single health care system was retrospectively analyzed. The primary outcome for analysis was indication-specific, risk-standardized CT utilization. We constructed seven clinical cohorts on the basis of the presence or absence of a traumatic indication for the most frequently performed CT studies. Risk standardization was performed using machine learning algorithms and hierarchic logistic regression models. Variation in CT utilization for each cohort was analyzed using coefficients of variation and box plots, the effect of risk standardization on physician profiling was determined using slope diagrams and kappa values, and within-physician correlation was assessed using correlation coefficients and matrices.

For the seven cohorts, the number of physicians ordering more than 25 CT studies for a particular indication ranged from 70 to 88, and the number of ED visits ranged from 17,458 to 117,489. The unadjusted variation was large for each indication (coefficient of variation, 30.2-57.9). Risk standardization resulted in reduced but persistent variation for all indications (coefficient of variation, 12.3-22.3). Among indication-specific models, risk standardization resulted in reclassification by two or more deciles for 14.0-39.1% of physicians. The R value for within-physician correlation varied from 0.02 to 0.80 and was highest between chest and abdominal imaging for trauma.

In this multisite study of CT utilization, risk standardization had a substantial impact on variation in CT utilization and emergency physician profiling. Administrators and payers should include risk standardization in future measures of physician imaging to ensure valid assessment of performance and achieve improvements in emergency care value.