Health System Affiliation and Care for Dual-Eligible and Non–Dual-Eligible Medicare Beneficiaries

Importance Physician organization (PO) affiliation with health systems and its association with health care disparities for dual-eligible Medicare and Medicaid beneficiaries, who face significant barriers to care, remains underexplored. Objectives To estimate the association of health system affiliation with disparities in quality of care and health care utilization for dual-eligible beneficiaries relative to non–dual-eligible Medicare beneficiaries and to decompose these associations into within-PO and between-PO components. Design, Setting, and Participants This cohort study used data from 2013 to 2019 on primary care POs and beneficiaries enrolled in traditional Medicare. Statistical analysis was performed from April 2024 to March 2025. Exposures Affiliation with health systems, defined as ownership or management relationships, using Medicare Provider Enrollment, Chain, and Ownership System data and Internal Revenue Service Form 990 data. Main Outcomes and Measures Eight quality measures assessing receipt of preventive services, chronic condition management, medication adherence, and care coordination and continuity and 5 measures of health care utilization in different settings and with different physician specialists. Linear mixed-effects models were used to estimate changes in disparities before and after affiliation for primary care POs between 2013 and 2019. Results A total of 5005 primary care POs and more than 5.6 million Medicare beneficiaries (mean [SD] age, 75.5 [7.5] years; 58.4% women) were analyzed, including approximately 700 000 dual-eligible beneficiaries. Affiliation with health systems was associated with widened disparities in diabetic eye examinations (3.5 percentage point larger relative reduction for dual-eligible beneficiaries compared with non–dual-eligible beneficiaries) and follow-up visits after acute events (3.5 percentage point larger relative reduction). On the other hand, dual-eligible beneficiaries experienced relative improvements in continuity of care with primary care clinicians (1.9 percentage points) and POs (1.4 percentage points) compared with non–dual-eligible beneficiaries, as well as larger relative improvements in statin prescribing (1.8 percentage points), widening preaffiliation differences that favored dual-eligible beneficiaries. Four of these 5 measures were associated with widening within-PO and between-PO disparities. Despite moderate and large preaffiliation disparities in primary care clinician visits and specialist visits, respectively, for dual-eligible beneficiaries relative to non–dual-eligible beneficiaries, disparities in primary care clinician visits widened (21 fewer visits per 100 beneficiaries) while disparities in specialist visits did not change meaningfully. Conclusions and Relevance In this cohort study, health system affiliation by primary care POs was associated with both positive and negative associations with disparities for dual-eligible beneficiaries and did not reduce the largest preaffiliation disparities. Health systems must strengthen their care delivery models to expand access to specialists and avoid exacerbating disparities in follow-up care. Health systems could identify factors associated with improved care at high-percentage dual POs for replication.