Mortality and Hospitalizations for Dually Enrolled and Nondually Enrolled Medicare Beneficiaries Aged 65 Years or Older, 2004 to 2017.

Importance: Medicare beneficiaries who are also enrolled in Medicaid (dually enrolled beneficiaries) have drawn the attention of policy makers because they comprise the poorest subset of the Medicare population; however, it is unclear how their outcomes have changed over time compared with those only enrolled in Medicare (nondually enrolled beneficiaries). Objective: To evaluate annual changes in all-cause mortality, hospitalization rates, and hospitalization-related mortality among dually enrolled beneficiaries and nondually enrolled beneficiaries. Design, Setting, and Participants: Serial cross-sectional study of Medicare fee-for-service beneficiaries aged 65 years or older between January 2004 and December 2017. The final date of follow-up was September 30, 2018. Exposures: Dual vs nondual enrollment status. Main Outcomes and Measures: Annual all-cause mortality rates; all-cause hospitalization rates; and in-hospital, 30-day, 1-year hospitalization-related mortality rates. Results: There were 71 017 608 unique Medicare beneficiaries aged 65 years or older (mean age, 75.6 [SD, 9.2] years; 54.9% female) enrolled in Medicare for at least 1 month from 2004 through 2017. Of these beneficiaries, 11 697 900 (16.5%) were dually enrolled in Medicare and Medicaid for at least 1 month. After adjusting for age, sex, and race, annual all-cause mortality rates declined from 8.5% (95% CI, 8.45%-8.56%) in 2004 to 8.1% (95% CI, 8.05%-8.13%) in 2017 among dually enrolled beneficiaries and from 4.1% (95% CI, 4.08%-4.13%) in 2004 to 3.8% (95% CI, 3.76%-3.79%) in 2017 among nondually enrolled beneficiaries. The difference in annual all-cause mortality between dually and nondually enrolled beneficiaries increased between 2004 (adjusted odds ratio, 2.09 [95% CI, 2.08-2.10]) and 2017 (adjusted odds ratio, 2.22 [95% CI, 2.21-2.23]) (P < .001 for interaction between dual enrollment status and time). All-cause hospitalizations per 100 000 beneficiary-years declined from 49 888 in 2004 to 41 121 in 2017 among dually enrolled beneficiaries (P < .001) and from 29 000 in 2004 to 22 601 in 2017 among nondually enrolled beneficiaries (P < .001); however, the difference between these groups widened between 2004 (adjusted risk ratio, 1.72 [95% CI, 1.71-1.73]) and 2017 (adjusted risk ratio, 1.83 [95% CI, 1.82-1.83]) (P < .001 for interaction). Among hospitalized beneficiaries, the risk-adjusted 30-day mortality rates declined from 10.3% (95% CI, 10.22%-10.33%) in 2004 to 10.1% (95% CI, 10.02%-10.20%) in 2017 among dually enrolled beneficiaries and from 8.5% (95% CI, 8.50%-8.56%) in 2004 to 8.1% (95% CI, 8.06%-8.13%) in 2017 among nondually enrolled beneficiaries. In contrast, 1-year mortality increased among hospitalized beneficiaries from 23.1% (95% CI, 23.05%-23.20%) in 2004 to 26.7% (95% CI, 26.58%-26.84%) in 2017 among dually enrolled beneficiaries and from 18.1% (95% CI, 18.11%-18.17%) in 2004 to 20.3% (95% CI, 20.21%-20.31%) in 2017 among nondually enrolled beneficiaries. The difference in hospitalization-related outcomes between dually and nondually enrolled beneficiaries persisted during the study period. Conclusions and Relevance: Among Medicare fee-for-service beneficiaries aged 65 years or older, dually enrolled beneficiaries had higher annual all-cause mortality, all-cause hospitalizations, and hospitalization-related mortality compared with nondually enrolled beneficiaries. Between 2004 and 2017, these differences did not decrease.