Medicare Advantage enrollees more likely to leave after new complex diagnosis

Medicare Advantage enrollees who developed a new complex condition, such as congestive heart failure or Alzheimer’s disease, were more likely to leave their plan for traditional Medicare the next year, according to a study published Aug. 21 in JAMA Health Forum.

Medicare Advantage (MA), the private alternative to traditional Medicare, covered 54% of Medicare beneficiaries in 2025, the study noted. MA plans offer perks traditional Medicare doesn't guarantee, such as spending caps and built-in drug coverage, but they also use prior authorization and limited networks that can slow down care. Folks with bigger health needs have left MA at higher rates than healthier enrollees.

However, leaving isn't simple. In most states, insurers don't have to sell Medigap, the supplemental coverage that fills traditional Medicare’s gaps, to someone who skipped it when they first signed up. That can leave beneficiaries who get sick later stuck without that backup option.

The study was led by Mark K. Meiselbach, Ph.D., of the Department of Health Policy and Management at Johns Hopkins Bloomberg School of Public Health, and his team, who said past studies treated a new diagnosis as simply yes-or-no and mostly tracked switches to traditional Medicare. The researchers wanted to see whether leaving MA increases with the number of new conditions a person develops and to separate switches to traditional Medicare from switches to a different MA plan, something earlier research hadn't done.

The retrospective cohort study used Medicare enrollment and claims data from 2016 through 2021, analyzed in late 2025 and early 2026. Researchers tracked beneficiaries who stayed in an MA plan all of 2016 and had no complex condition through 2018. Using a standard federal algorithm, they flagged eight conditions: heart attack, Alzheimer disease, atrial fibrillation, chronic kidney disease, chronic obstructive pulmonary disease (COPD), depression, congestive heart failure and stroke.

A treatment group of 219,942 beneficiaries developed one of those conditions in 2019; a comparison group of 834,984 did not develop one through 2021. Using a difference-in-differences design, researchers compared how disenrollment changed for each group before and after 2019, then checked whether that change depended on how many new conditions someone developed, their state's Medigap rules, and whether their MA plan was a health maintenance organization (HMO).

Developing any new complex condition raised MA disenrollment by 3.3 percentage points. Almost all of that increase came from people leaving for traditional Medicare rather than switching to a different MA plan. The more conditions someone developed, the more likely they were to leave: 1.4 percentage points with one new condition, up to 12.8 points among the 1,010 people with four or more. A new Alzheimer’s disease diagnosis had the single biggest effect, an 8.6 percentage point increase, while the rest ranged from 2.9 to 5.0 points.

Beneficiaries in the four states with Medigap guaranteed-issue and community-rating rules, Connecticut, Maine, Massachusetts and New York, were 1.5 percentage points more likely to leave for traditional Medicare than beneficiaries elsewhere. Those enrolled in HMO plans were less likely to leave for traditional Medicare but more likely to switch to a different MA plan.

Dual-eligible beneficiaries, who qualify for both Medicare and Medicaid, left for traditional Medicare at higher rates and switched MA plans less often, which the authors said tracks with Medicaid reducing their need for Medigap. Plan star ratings didn't matter much: those in 4- or 5-star plans left at about the same rate as those in 3-star plans after a new diagnosis, suggesting star ratings don't capture how well a plan serves sicker members.

"These findings underscore the difficulty of making an initial enrollment decision in Medicare," the study's authors wrote in the discussion. "Beneficiaries cannot foresee all of their future health needs when they first enroll in MA, but the consequences of that decision may depend on health events that occur years later."

Strengths in this study include the tracked disenrollment trends before 2019, not just a single before-and-after comparison, and the study found no sign the groups were already diverging. The results also held up after adjusting for other chronic conditions people developed.

However, there are limits. Since new conditions were identified from claims, which usually show up after a diagnosis, the authors said their numbers likely undercount the true effect rather than overstate it. Counting conditions is also an imperfect stand-in for true complexity, and the group with four or more new conditions was small, just 1,010 people, so those figures carry more uncertainty. The data ends in 2021 and doesn’t reflect newer MA plan designs.

The authors confirmed that state Medigap protections make it easier for more ill beneficiaries to switch to traditional Medicare, but expanding those protections more broadly could push Medigap premiums up for everyone. And MA star ratings, as they currently work, may not reflect how well a plan actually serves members whose health needs have grown more complex.