Impact of the California Breast Density Law on Screening Breast MR Utilization, Provider Ordering Practices, and Patient Demographics

Purpose: To assess the impact of California's Breast Density Law (BDL) on MRI utilization and clinician ordering practices. Materials and Methods: Our institutional review board approved this study that retrospectively compared the ordering pattern for screening breast MRI examinations in the 30-month period before and after the BDL was enacted. Examinations were subcategorized into those with breast density mentioned as an examination indication. Patients were classified into (1) high risk; (2) above average risk, defined but not quantified; and (3) undefined or average risk. χ² test or Fisher's exact test was used to compare MRI utilization, use of breast density as an indication, patient demographics, and provider characteristics. Results: Screening MRI examinations with breast density as the indication increased from 8.5% (32 of 376) to 21.1% (136 of 646, P <.0001) after BDL. When high-risk patients were excluded, the increase was from 8% to 17.2% (P <.0001). Patient demographics before and after BDL were, by race: white 71.8% versus 71.2%; Asian 6.4% versus 10.5%; black 3.7% versus 3.1%; American Indian 0.3% versus 1.4%; Native Hawaiian or Pacific Islander 1.6% versus 1.7%; by ethnicity: Hispanic or Latino 10.6% versus 7.9%. Before and after BDL, predominantly female providers (81.4% and 77.4%, P = not significant [NS]) and specialists (62.5% and 63.5%, P = NS) ordered the majority of breast MRI examinations compared with males (18.6% and 22.6%, P = NS). Conclusion: Screening breast MRI utilization for non-high-risk women more than doubled after the California BDL went into effect. BDL has had an impact on MRI utilization, and its clinical value for changing outcomes deserves further study.