• Eili Y Klein, Scott Levin, Matthew F Toerper, Michael D Makowsky, Tim Xu, Gai Cole, and Gabor D Kelen.
• Department of Emergency Medicine, Baltimore, MD; Center for Disease Dynamics, Economics and Policy, Washington, DC. Electronic address: eklein@jhu.edu.
• Ann Emerg Med. 2017 Nov 1; 70 (5): 607-614.e1.

Study ObjectiveA proposed benefit of expanding Medicaid eligibility under the Patient Protection and Affordable Care Act (ACA) was a reduction in emergency department (ED) utilization for primary care needs. Pre-ACA studies found that new Medicaid enrollees increased their ED utilization rates, but the effect on system-level ED visits was less clear. Our objective was to estimate the effect of Medicaid expansion on aggregate and individual-based ED utilization patterns within Maryland.MethodsWe performed a retrospective cross-sectional study of ED utilization patterns across Maryland, using data from Maryland's Health Services Cost Review Commission. We also analyzed utilization differences between pre-ACA (July 2012 to December 2013) uninsured patients who returned post-ACA (July 2014 to December 2015).ResultsThe total number of ED visits in Maryland decreased by 36,531 (-1.2%) between the 6 quarters pre-ACA and the 6 quarters post-ACA. Medicaid-covered ED visits increased from 23.3% to 28.9% (159,004 additional visits), whereas uninsured patient visits decreased from 16.3% to 10.4% (181,607 fewer visits). Coverage by other insurance types remained largely stable between periods. We found no significant relationship between Medicaid expansion and changes in ED volume by hospital. For patients uninsured pre-ACA who returned post-ACA, the adjusted visits per person during 6 quarters was 2.38 (95% confidence interval 2.35 to 2.40) for those newly enrolled in Medicaid post-ACA compared with 1.66 (95% confidence interval 1.64 to 1.68) for those remaining uninsured.ConclusionThere was a substantial increase in patients covered by Medicaid in the post-ACA period, but this did not significantly affect total ED volume. Returning patients newly enrolled in Medicaid visited the ED more than their uninsured counterparts; however, this cohort accounted for only a small percentage of total ED visits in Maryland.Copyright © 2017 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved.

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