Medicare Advantage in the US Mainland and Puerto Rico

ABSTRACT

Objectives: To compare enrollment rates in Medicare Advantage (MA) among people with disabilities (PWD) and individuals with end-stage renal disease (ESRD) in the US (50 states and District of Columbia) and Puerto Rico (PR).

Study Design: This observational study utilized repeated cross-sectional data from the Master Beneficiary Summary File from 2008 to 2022.

Methods: The sample included beneficiaries who had continuous Medicare enrollment during the corresponding calendar year and were alive at the end of March 31 the following year. Partial-year MA enrollment was defined as having at least 1 month of MA coverage. Full-year MA enrollment was defined as having continuous MA coverage for all 12 months. We calculated the percentage of enrollees in MA based on their entitlement (age, disability, and ESRD). Standardized differences were calculated to compare characteristics of US and PR enrollees in 2022.

Results: Between 2008 and 2022, our study included 757,245,942 person-years from the US and 10,298,906 person-years from PR. In 2022, Medicare beneficiaries in PR exhibited a higher partial-year MA enrollment rate—nearly double that of the US (84% vs 48%; d = 0.837; 95% CI, 0.835-0.839). In addition, in the US, the difference between partial-year and full-year MA enrollment rates was 5.7% for PWD and 9.1% for ESRD enrollees. In PR, the differences were 2.7% for PWD and 10.0% for ESRD enrollees.

Conclusions: Discrepancies between partial-year and full-year MA enrollment persisted among PWD and ESRD subpopulations, highlighting potential differences in coverage and access to care for these groups.

Am J Manag Care. 2026;32(2):In Press

Takeaway Points

This observational study utilized repeated cross-sectional data from the 100% Master Beneficiary Summary File from 2008 to 2022 to identify Medicare Advantage (MA) enrollment by current Medicare entitlement in the US and Puerto Rico.

• Our results indicate growth in MA enrollment in the US mainland and Puerto Rico, particularly among people with disabilities (PWD) and individuals with end-stage renal disease (ESRD).
• Among PWD and individuals with ESRD, full-year (12-month) MA enrollment was lower than partial-year (any-month) enrollment in both the US mainland and Puerto Rico.
• Discrepancies between partial-year and full-year MA enrollment among PWD and ESRD subpopulations may reflect changes in plan choice, access to care, and care quality.

Under the Balanced Budget Act of 1997, Medicare Advantage (MA), originally known as Medicare+Choice (Part C), began offering coverage for individuals 65 years and older and for younger people with disabilities (PWD).^1,2 As of January 1, 2021, the 21st Century Cures Act expanded enrollment of individuals with end-stage renal disease (ESRD) in MA plans by allowing them to choose between MA or fee-for-service Medicare plans.³ Enrollment in MA increased among individuals with ESRD during the first 2 years of the 21st Century Cures Act.⁴ However, there is limited information on enrollment rates in MA among these high-need populations, specifically when comparing enrollees with 12-month enrollment vs those with any MA enrollment during the year (ie, at least 1 month). Assessing these 2 measures simultaneously may reflect changes in insurance preferences, access to care, and care quality that may result in switching from MA to fee-for-service. Thus, this study compared the MA enrollment rates of PWD and individuals with ESRD in the US (50 states and the District of Columbia) and Puerto Rico (PR) from 2008 to 2022.

METHODS

This observational study utilized repeated cross-sectional data from the Master Beneficiary Summary File from 2008 to 2022 to identify MA enrollment, current Medicare entitlement, state of residence, and demographic characteristics. The inclusion criteria were full-year Medicare enrollment in the corresponding calendar year and being alive until the end of March 31 the following year. The MA enrollment rate was calculated based on 2 criteria: (1) Partial-year MA enrollment was defined as having at least 1 month of MA coverage, including individuals who switched between fee-for-service and MA during the year; and (2) full-year MA enrollment was defined as having continuous MA coverage for all 12 months. Standardized differences (d) were calculated to compare characteristics between enrollees who met the inclusion criteria and were residing in either the US or PR in 2022. The study protocol was approved by the Brown University Institutional Review Board.

RESULTS

Our study included 757,245,942 person-years in the US and 10,298,906 person-years in PR from 2008 to 2022. The Table^5,6 summarizes the demographic characteristics of all Medicare beneficiaries who met the inclusion criteria and were residing in the US or PR in 2022. There were moderate to large differences in MA penetration (d = 0.763; 95% CI, 0.760-0.765) and enrollment rate (d = 0.837; 95% CI, 0.835-0.839) between US enrollees and PR enrollees in 2022 (Table). In 2022, Medicare beneficiaries in PR exhibited a strikingly higher partial-year MA enrollment rate compared with beneficiaries in the US (84% vs 48%). MA enrollment has steadily increased, particularly among the PWD and ESRD subpopulations, in both the US and PR (Figure). For the overall MA enrollment rate, the differences observed between the proportion of full-year and partial-year MA enrollment were 2.8% in the US and 1.9% in PR in 2022. However, larger discrepancies were observed among the PWD and ESRD subpopulations in 2022. In the US, the differences between partial-year and full-year MA enrollment rates were 5.7% for PWD and 9.1% for ESRD enrollees. In PR, the differences were 2.7% for PWD and 10.0% for ESRD enrollees.

DISCUSSION

Differences between partial-year and full-year MA enrollment among patients with ESRD may reflect changes in plan choice, access, and continuity of care. High poverty rates in PR may make MA plans particularly attractive to high-need beneficiaries due to their ability to offer lower premiums and supplemental benefits addressing social determinants of health and to the vast majority of dually eligible beneficiaries receiving care through local MA plans, accounting for a high share of MA enrollment.⁷ However, it is unclear whether differences in MA provider networks and benefit design may further impact disparities in nephrology care for patients with kidney failure and access to postacute rehabilitation in PR compared with the US.^8,9 Given the differences in partial-year and full-year MA enrollment among individuals with ESRD, especially in PR, assessing key factors influencing plan choice and switching, as well as the impact of MA on quality of care and outcomes, may be needed. 

Author Affiliations: Department of Physical Therapy and Athletic Training, University of Utah College of Health (LNC, AK), Salt Lake City, UT; Department of Health Services, Policy, and Practice, Brown University School of Public Health (MR-H), Providence, RI.

Source of Funding: This study was supported by the National Institute on Aging of the National Institutes of Health (K01AG057822; RF1AG078262; R01MD016961; R01MD017719) and a Research Seed Award from Brown University Office of the Vice President. The National Institutes of Health had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.

Author Disclosures: Dr Rivera-Hernandez has received grants from the National Institutes of Health, received honoraria from the Oklahoma Dementia Care Network (sponsored by the Health Resources and Services Administration Geriatrics Workforce Enhancement Program and HHS through the Building Our Largest Dementia Infrastructure for Alzheimer’s Act), and attended the Oklahoma Dementia Care Network Annual Innovations in Aging Conference and AcademyHealth and Gerontological Society of America meetings. The remaining authors report no relationship or financial interest with any entity that would pose a conflict of interest with the subject matter of this article.

Authorship Information: Concept and design (LNC, AK, MR-H); analysis and interpretation of data (LNC, AK, MR-H); drafting of the manuscript (LNC, AK); critical revision of the manuscript for important intellectual content (LNC, AK, MR-H); statistical analysis (LNC); obtaining funding (AK, MR-H); administrative, technical, or logistic support (AK); and supervision (AK).

Address Correspondence to: Maricruz Rivera-Hernandez, PhD, Department of Health Services, Policy, and Practice, Brown University, 121 S Main St, Providence, RI 02903. Email: maricruz_rivera-hernandez@brown.edu.

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