Older adults with newer, more complex medical conditions were more likely to leave a Medicare Advantage plan for traditional Medicare, and this likelihood increased as medical complexity increased, according to a new study released Friday.
The study published in the JAMA Health Forum builds on earlier research showing that people who develop serious illnesses, including cancer, were more likely to leave MA.
In the latest exploration, the researchers wanted to look more closely at how the number and complexity of new medical conditions affect disenrollment from MA plans. They were particularly interested in whether becoming sicker makes people more likely to leave their MA plan and whether they return to traditional Medicare or simply switch to another MA plan.
“In this cohort study, developing a new complex medical condition was associated with higher disenrollment from an MA plan, particularly to [traditional Medicare], and the difference-in-differences estimates increased with the number of complex conditions,” the authors wrote
Disenrollment to traditional Medicare was particularly higher among enrollees living in states with Medigap community-rating and guaranteed-issue protections, the study found, because the Medigap protections make switching to traditional Medicare easier for those with the greatest levels of medical complexity enrolled in MA.
Medigap coverage is private insurance that helps cover costs not paid by traditional Medicare and community-rating protections limit how much insurers can vary Medigap premiums based on factors such as age and health, while guaranteed-issue protections require insurers, in certain circumstances, to offer coverage regardless of health status
Disenrollment within MA was higher among beneficiaries enrolled in health maintenance organizations (HMOs), the findings also state
The study used Medicare enrollment and medical claims data from 2016 through 2021. It followed people who were continuously enrolled in Medicare Advantage and had no complex medical conditions from 2016 to 2018. The researchers then compared those who developed a new complex condition in 2019 with those who did not develop one through 2021. The data were analyzed between December 2025 and March 2026.
Additional plan information, including the plan type, such as HMO or other plan type, were obtained from Centers for Medicare and Medicaid Services (CMS) public use files.
Complex conditions included in the study’s examination included acute myocardial infarction, Alzheimer disease and related disorders, atrial fibrillation, chronic kidney disease, chronic obstructive pulmonary disease and asthma, depression, congestive heart failure, or stroke
“We selected this list of complex conditions as they have been identified as conditions that segment high-cost Medicare beneficiaries into clinically coherent cohorts with elevated care needs, and because they have been used in prior studies examining MA disenrollment,” the researchers wrote.
The vast majority of Medicare Advantage (MA) enrollees, or about 90%, are aged 65 or older, according to MedPAC’s 2026 figures. Overall, 32.8 million people are enrolled in MA plans.
MA enrollment among nursing-home residents has grown substantially. In 2023, 36.5% of long-stay nursing-home residents were enrolled in MA, according to data in the Journal of the American Geriatrics Society
