Hospital emergency departments (EDs) have a vital role in our health care system. As the only guaranteed access point to medical care for all Californians, they are often characterized as the safety net of the safety net. But they are also a relatively expensive setting to provide health services. A substantial uptick in ED use over the past several years has raised questions about the impact of the Affordable Care Act (ACA). In particular, the large expansion of the Medi-Cal program under the ACA has raised concerns that the dramatic declines in uninsured residents in such a short timeframe may be spurring increases in ED use.

In this report, we look at trends in ED use from 2005 to 2016, with a particular focus on rates of ED use since ACA insurance expansions were fully implemented in 2014. We find no evidence that the ACA was responsible for increased ED use-indeed, our analysis suggests that ED visit rates for non-elderly adults would have been higher in the absence of the coverage expansions.

Our key findings include:

• Large reductions in the number of uninsured Californians as a result of the 2014 ACA expansion of major insurance coverage options did not increase ED use among adults under age 65, and may in fact have reduced ED use among middle-age adults ages 35-54.
• Among non-elderly adults, women age 19-34 have the highest rates of ED use (42 visits per 100 population in 2016), at least partly due to pregnancy-related visits.
• The vast majority (about 90%) of all ED visits made by adults under age 65 are outpatient visits-patients are treated and released the same day. Only about 10 percent of ED visits result in admission to the hospital.
• ED outpatient use has increased substantially across all demographic groups and for all reasons. Non-elderly adults experienced the largest uptick, increasing by 38 percent between 2005 and 2016.

While our findings on the impact of the ACA are encouraging, the growing use of EDs for complex needs requires closer consideration of how EDs fit into our evolving health care system. Medi-Cal has a key role to play in monitoring and managing ED use. This is both because one in three Californians has health insurance through the Medi-Cal program and because Medi-Cal enrollees have higher visit rates compared to those with private coverage and the uninsured.

More broadly, as state policymakers contemplate further insurance expansions with an eye toward universal coverage, it will be essential to continue monitoring patterns of health care use and to carefully evaluate efforts aimed at curbing ED use.