Out-of-pocket spending and financial burden among low income adults after Medicaid expansions in the United States: quasi-experimental difference-in-difference study.

Objective: To examine the association between expansion of the Medicaid program under the Affordable Care Act and changes in healthcare spending among low income adults during the first four years of the policy implementation (2014-17).

Design: Quasi-experimental difference-in-difference analysis to examine out-of-pocket spending and financial burden among low income adults after Medicaid expansions.

Setting: United States.

Participants: A nationally representative sample of individuals aged 19-64 years, with family incomes below 138% of the federal poverty level, from the 2010-17 Medical Expenditure Panel Survey.

Main Outcomes And Measures: Four annual healthcare spending outcomes: out-of-pocket spending; premium contributions; out-of-pocket plus premium spending; and catastrophic financial burden (defined as out-of-pocket plus premium spending exceeding 40% of post-subsistence income). P values were adjusted for multiple comparisons.

Results: 37 819 adults were included in the study. Healthcare spending did not change in the first two years, but Medicaid expansions were associated with lower out-of-pocket spending (adjusted percentage change -28.0% (95% confidence interval -38.4% to -15.8%); adjusted absolute change -$122 (£93; €110); adjusted P<0.001), lower out-of-pocket plus premium spending (-29.0% (-40.5% to -15.3%); -$442; adjusted P<0.001), and lower probability of experiencing a catastrophic financial burden (adjusted percentage point change -4.7 (-7.9 to -1.4); adjusted P=0.01) in years three to four. No evidence was found to indicate that premium contributions changed after the Medicaid expansions.

Conclusion: Medicaid expansions under the Affordable Care Act were associated with lower out-of-pocket spending and a lower likelihood of catastrophic financial burden for low income adults in the third and fourth years of the act's implementation. These findings suggest that the act has been successful nationally in improving financial risk protection against medical bills among low income adults.