ACA coverage expansion decreased frequent ED use among Medicaid, uninsured patients

Under the Affordable Care Act (ACA), the share of all California ED patients covered by Medicaid increased from 21.5% to 37.6%, and the share of uninsured patients decreased from 26.9% to 13.2%, the study found.


California patients with Medicaid coverage or without insurance were less likely to be frequent ED users after the Affordable Care Act (ACA) expanded coverage compared to the prior two-year period, a recent study found.

Using 2012 to 2015 data from California's Office of Statewide Health Planning and Development, researchers compared characteristics of the state's frequent ED users ages 18 to 64 years before (2012 and 2013) and after (2014 and 2015) implementation of several ACA provisions that expanded health care coverage. Frequent users were defined as patients with four or more ED visits in a single calendar year. Results were published June 4 by Health Affairs.

Under the ACA, the share of all ED patients covered by Medicaid increased from 21.5% to 37.6%, and the share of uninsured patients decreased from 26.9% to 13.2%. These changes were even more pronounced among frequent ED users, with the proportion covered by Medicaid increasing from 44.6% to 67.6% and the proportion of uninsured decreasing from 29.0% to 8.3%.

In the two years after coverage expansion, the number of ED users increased by 511,284 (7.7%) compared to the two years prior, and the number of ED visits increased by about 1.16 million (9.9%). The number of frequent ED users increased by 81,800 under the ACA, accounting for 8.5% of ED patients compared to 7.9% of ED patients in 2012 and 2013. Frequent ED users comprised 30.7% of all ED visits before and 31.6% of those after coverage expansions took effect.

However, after controlling for patient characteristics such as health status, primary insurance coverage source, and county of residence, researchers found that the odds of being a frequent ED user declined by 12% for Medicaid patients and by nearly 50% for uninsured patients. Patients with private insurance saw a slight increase in the odds of frequent ED use, although they had much lower baseline odds of frequent use. The largest predictors of frequent ED use were diagnosis of a mental health condition (odds ratio, 3.34; P<0.001) and diagnosis of a non-alcohol-related substance use disorder (odds ratio, 2.64; P<0.001).

The study authors noted limitations of the analysis, such as how the data were self-reported by hospitals, potentially introducing errors and omissions. They added that 12% of ED visits could not be linked to individual patients and that the results apply only to California, which runs the largest Medicaid program in the country. The authors noted that although some were concerned that frequent ED use would rise with expanded coverage, “Our results suggest that the opposite occurred.”