Use of diagnostic imaging studies and associated radiation exposure for patients enrolled in large integrated health care systems, 1996-2010

Abstract

Context: Use of diagnostic imaging has increased significantly within fee-for-service models of care. Little is known about patterns of imaging among members of integrated health care systems.

Objective: To estimate trends in imaging utilization and associated radiation exposure among members of integrated health care systems.

Design, setting, and participants: Retrospective analysis of electronic records of members of 6 large integrated health systems from different regions of the United States. Review of medical records allowed direct estimation of radiation exposure from selected tests. Between 1 million and 2 million member-patients were included each year from 1996 to 2010.

Main outcome measure: Advanced diagnostic imaging rates and cumulative annual radiation exposure from medical imaging.

Results: During the 15-year study period, enrollees underwent a total of 30.9 million imaging examinations (25.8 million person-years), reflecting 1.18 tests (95% CI, 1.17-1.19) per person per year, of which 35% were for advanced diagnostic imaging (computed tomography [CT], magnetic resonance imaging [MRI], nuclear medicine, and ultrasound). Use of advanced diagnostic imaging increased from 1996 to 2010; CT examinations increased from 52 per 1000 enrollees in 1996 to 149 per 1000 in 2010, 7.8% annual increase (95% CI, 5.8%-9.8%); MRI use increased from 17 to 65 per 1000 enrollees, 10% annual growth (95% CI, 3.3%-16.5%); and ultrasound rates increased from 134 to 230 per 1000 enrollees, 3.9% annual growth (95% CI, 3.0%-4.9%). Although nuclear medicine use decreased from 32 to 21 per 1000 enrollees, 3% annual decline (95% CI, 7.7% decline to 1.3% increase), PET imaging rates increased after 2004 from 0.24 to 3.6 per 1000 enrollees, 57% annual growth. Although imaging use increased within all health systems, the adoption of different modalities for anatomic area assessment varied. Increased use of CT between 1996 and 2010 resulted in increased radiation exposure for enrollees, with a doubling in the mean per capita effective dose (1.2 mSv vs 2.3 mSv) and the proportion of enrollees who received high (>20-50 mSv) exposure (1.2% vs 2.5%) and very high (>50 mSv) annual radiation exposure (0.6% vs 1.4%). By 2010, 6.8% of enrollees who underwent imaging received high annual radiation exposure (>20-50 mSv) and 3.9% received very high annual exposure (>50 mSv).

Conclusion: Within integrated health care systems, there was a large increase in the rate of advanced diagnostic imaging and associated radiation exposure between 1996 and 2010.

Figure 1

Imaging examinations per 1000 enrollees, by modality and year, adjusted to a standard age distribution across sites and years. Each line reflects a single health plan.

Figure 2

Imaging examinations per 1000 enrollees by modality, age and year. All results adjusted to a standard age distribution. Each cluster of lines reflects changing rates of imaging over time within age strata.

Figure 3

a. Annual average effective dose received by the highest 1% of health plan member-enrollees by health plan and year. Each line reflects a single health plan. b. Annual average effective dose received by the highest 10% of health plan member-enrollees by health plan and year. Each line reflects a single health plan. Footnote. The 95% confidence intervals were narrow. We calculated the average effective dose received by the highest 1% of health plan members across all sites, and the 95% confidence interval had a width < 2mSv for Figure 3a and < .1 mSv for Figure 3b.