• Tim Xu, Eili Y Klein, Mo Zhou, Justin Lowenthal, Joshua M Sharfstein, and Susan M Peterson.
• Department of Emergency Medicine, Johns Hopkins University School of Medicine, and the Department of Health Policy and Management, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD. Electronic address: tim.xu@jhmi.edu.
• Ann Emerg Med. 2018 Aug 1; 72 (2): 156-165.

Study ObjectiveWe analyzed the effect of insurance expansion on emergency department (ED) utilization among the uninsured in Maryland, which expanded Medicaid eligibility and created health insurance exchanges in 2014.MethodsThis was a retrospective analysis of statewide administrative claims for July 2012 to December 2015. We used coarsened exact matching to pair uninsured and insured (Medicaid, Medicare, commercial, and other) adult Maryland residents who visited an ED or were hospitalized at baseline (July 2012 to December 2013). We compared ED utilization between these groups after insurance expansion (January 2014 to December 2015), using a difference-in-differences quasi-experimental design. Nonreturning patients from the baseline period were included in the post-insurance expansion rates as having zero visits.ResultsMatching yielded 178,381 pairs. In the 12 months before insurance expansion, the baseline uninsured group visited the ED at a rate of 26.1 per 100 patient-quarters versus 28.2 among the insured group (relative rate=0.93). In the 24 months after insurance expansion, 45% of the baseline uninsured returned to an ED, of whom 33% returned uninsured, 40% returned with Medicaid, and 21% returned with commercial insurance. After insurance expansion, with 55% of patients in each group not returning, the ED visit rate for both the baseline uninsured and insured groups was 15.9 per 100 patient-quarters (relative rate=1.00). This 8% relative increase from baseline in ED visits among the uninsured group was driven primarily by increases in higher-acuity visits. Uninsured patients from high-poverty zip codes (N=34,964 pairs) increased their ED utilization by 15% after insurance expansion, whereas baseline uninsured patients with no comorbidities (N=94,330 pairs) showed a 3% decrease.ConclusionInsurance expansion in Maryland was associated with a modest relative increase in ED visits among the uninsured, driven by increases in higher-acuity visits. It remains unclear whether insurance coverage helped the uninsured address their unmet medical needs.Copyright © 2018 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved.

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