PROJECT SUMMARY Among the 10,000 Americans turning 65 every day, those with health insurance coverage under the Affordable Care Act's Medicaid expansion face a unique challenge: They may lose Medicaid coverage when they transition to Medicare as their primary insurer and face substantially higher premium and out-of-pocket costs. This transition in insurance coverage may have deleterious effects on access to care, but there is little published research to our knowledge about the individuals who “age out” of Medicaid expansion coverage and transition to Medicare as their primary insurer. The long-term goal of this proposal is to inform policies to ensure that adults with low incomes have access to comprehensive, affordable health care whether they are nearing age 65 or are on the other side of it. The immediate objective of this research is to understand the extent to which 64-year-old Medicaid expansion enrollees lose or retain Medicaid benefits upon transitioning to Medicare and how this impacts their risk of hospitalization and even death. Our central hypotheses are that many near-elderly adults with Medicaid expansion coverage do not retain full Medicaid benefits when they turn 65, particularly in states with less generous dual eligibility criteria, and this negatively affects their ability to access care. To evaluate our hypotheses, we will address these specific aims: 1) Identify individual characteristics and state-level policies associated with the loss or retention of Medicaid coverage at age 65 among individuals who had coverage through Medicaid expansion as 64-year-olds, and 2) evaluate whether the loss of full Medicaid benefits upon transitioning to Medicare impacts acute hospitalizations and all-cause mortality in the first year of Medicare coverage and up to three years after transitioning. To achieve these aims, we propose to use 2014 and 2015 Medicaid enrollment and claims data for eight large Medicaid expansion states (California, Illinois, Maryland, Massachusetts, New Jersey, New York, Ohio, and Pennsylvania) to identify a cohort of 64-year-olds that can be linked to Medicare enrollment and claims data through 2018. The first aim will apply a longitudinal study design to examine patterns of loss and retention of Medicaid benefits among individuals who had Medicaid expansion coverage at age 64 and then transitioned to Medicare at age 65. Aim 2 will apply a quasi-experimental study design to compare the rate of acute hospitalizations and the mortality rate before and after the transition to Medicare at age 65 among the group of Medicaid expansion enrollees who retained Medicaid when they became Medicare beneficiaries, and among the group that lost Medicaid. This work is innovative because it will be the first study to link Medicaid and Medicare enrollment and claims data to study this population over time. This work is significant because it will reveal whether older adults with Medicaid expansion coverage may be worse off when they...