Quantifying health insurance eligibility impact on interhospital transfers of injured patients: Evidence from the affordable care act's dependent coverage provision

Background: Observational studies reported that nontrauma/low-level trauma centers less frequently transferred insured injured patients to high-level centers. The dependent coverage provision of the Affordable Care Act was a natural experiment expanding insurance eligibility in 2010 by allowing young adults to remain on their parents’ insurance until age 26 years old. The objective was to determine whether expanded insurance eligibility reduced interhospital transfers. Methods: This observational, retrospective cohort study of the 2007–2013 National Trauma Data Bank used a difference-in-differences design to compare the change in interhospital transfer rates before and after dependent coverage provision implementation between dependent coverage provision–eligible (aged 19–25 years) and dependent coverage provision–ineligible (aged 27–34 years) injured patients. The exposure of interest was the dependent coverage provision. The main outcome was yearly rate of interhospital transfer. Least-squares linear regression modeled interhospital transfer rates and quantified association with the age-based dependent coverage provision eligibility binary interaction term in the pre–dependent coverage provision versus post–dependent coverage provision time periods. Results: A total of 535,036 dependent coverage provision–eligible and 431,462 dependent coverage provision–ineligible patients were identified. The median Injury Severity Score was 6.0 (interquartile range = 4.0–13.0) for both cohorts. Private insurance rates increased from 28.1% to 38.7% among the dependent coverage provision–eligible cohort and from 27.0% to 30.5% among the older cohort between the pre–dependent coverage provision to post–dependent coverage provision time period. The average yearly interhospital transfer rate was not significantly different between the cohorts in the pre–dependent coverage provision (2.3% lower among dependent coverage provision–eligible) and the post–dependent coverage provision time periods (2.9% lower among dependent coverage provision–eligible). Difference-in-differences analysis revealed nonsignificant 14.6 fewer transfers/10,000 patients (95% confidence interval = 33.7 fewer to 4.4 more transfers/10,000 patients). Conclusion: Policies expanding insurance eligibility do not reduce interhospital transfers in a mature trauma system.