Trends in Preventable Inpatient and Emergency Department Utilization in California Between 2012 and 2015: The Role of Health Insurance Coverage and Primary Care Supply.

BACKGROUND: Expansions of health insurance coverage tend to increase hospital emergency department (ED) utilization and inpatient admissions. However, provisions in the Affordable Care Act that expanded primary care supply were intended in part to offset the potential for increased hospital utilization.
OBJECTIVES: To examine the association between health insurance coverage, primary care supply, and ED and inpatient utilization, and to assess how both factors contributed to trends in utilization in California between 2012 and 2015.
METHODS: Population-based measures of ED and inpatient utilization, insurance coverage, and primary care supply were constructed for California counties for the years 2012 through 2015. Fixed effects regression analysis is used to examine the association between health insurance coverage, primary care supply, and rates of preventable ED and inpatient utilization.
RESULTS: Higher levels of Medicaid coverage in a county are associated with higher levels of preventable ED and inpatient utilization, although greater numbers of primary care practitioners and Federally Qualified Health Centers reduce this type of utilization.
CONCLUSIONS: Increases in coverage accelerated a long-term increase in ED visits and prevented an even larger decrease in inpatient admissions, but changes in coverage do not fully explain these underlying trends. Increases in primary care supply offset the effects of coverage changes only modestly. Policymakers should not overstate the impact of the Affordable Care Act on increasing ED visits, and should focus on better understanding the underlying factors that are driving the trends.