LAUSR

STUDY OBJECTIVE We examine the effect of the Medicaid expansion in 2014 under in the Patient Protection and Affordable Care Act on emergency department (ED) utilization and ED admission rates (fraction of ED visits that lead to hospital admission) during the first 3 postexpansion years (2014 to 2016). METHODS We compared ED utilization and ED admission rates in 151 EDs in 14 expansion states with those in 376 EDs in 14 nonexpansion states, using difference-in-differences methods with data from 3 national emergency medicine groups from 2013 to 2016. RESULTS In expansion states, the volume of Medicaid-paid ED visits increased 49% (95% confidence interval 34% to 65%), and the volume of uninsured visits decreased 44% (95% confidence interval -52% to -34%) relative to that of nonexpansion states. Both effects on payer mix leveled off during 2015. There was no significant relative change in overall ED utilization or overall ED admission rates in expansion versus nonexpansion states during the study. However, relative ED admission rates for uninsured patients declined 8% (95% confidence interval -18% to -2%) in expansion states. CONCLUSION Large changes in payer mix in expansion versus nonexpansion states were observed but leveled off during 2015, with more Medicaid-paid visits and fewer uninsured visits in expansion states. Despite these large changes, during this 3-year period, there was no evidence that expansion affected either overall ED visit volume or ED admission rates. The relative decline in ED admission rates in expansion states among the uninsured may reflect a selection effect in which, among newly Medicaid-eligible persons, sicker persons were more likely to enroll than healthier ones.