The Effect of Medicaid Expansion on the Nature of New Enrollees' Emergency Department Use.

We examine changes in emergency department (ED) visit acuity and care intensity for uninsured patients who gained Medicaid insurance in 2014 under the Patient Protection and Affordable Care Act. We use 2013-2015 longitudinal patient visit-level data from 30 EDs across 7 states from an emergency medicine group. We examine changes in ED use by previously uninsured Medicaid patients and patients remaining uninsured who were repeat ED users (≥1 visit before and after expansion) using a propensity-score weighted approach with statistical machine learning to estimate the weights. Compared with those remaining uninsured in nonexpansion states, newly covered Medicaid patients in expansion states showed a 29% relative increase in hospital admissions and 32% increase in admissions for nonambulatory care sensitive conditions with no increases in care intensity. Obtaining Medicaid insurance increased the relative proportion of ED visits requiring hospital admission suggesting increased outpatient access for low-acuity conditions previously addressed with ED care.