Estimating the causal effect of the Medicaid expansion on heart transplant volume with a differences-in-differences...

Recent health policy changes have prioritized providing insurance for more Americans, often through Medicaid expansion (ME). The effectiveness of ME as it relates to expanding access to heart transplantation can be gauged by comparing the volume of Medicaid beneficiaries undergoing heart transplantation volume in states with and without ME. Our objective is to determine whether or not ME increased access to heart transplantation.

The Organ Procurement and Transplantation Network database was used for US transplant data. Difference-in-differences (DiD), an econometric method to estimate causality, was performed between states with ME and bordering states without ME, to minimize geographic variability. For states with multiple bordering nonexpanded states, DiD values were averaged. Unpaired 2-tailed t tests, Mann-Whitney U test, 1-way-analysis of variance, and Poisson regressions, where appropriate, compared insurance cohorts, sexes, and ethnicities.

Although publicly insured patients comprised only 36.7% of heart transplant volume in 2000, they comprised 53.4% of heart transplant volume in 2020 (P = .229); significant differences did not exist between public and private transplant volume (P = .583), but exist among forms of public insurance (P < .001). ME yielded 1.028 more transplants per state per year, and a total of 113.9 more transplants. Transplant volume was significantly different between ME states and non-ME states (31.4% vs 58.4%; P < .001). ME yielded 106 more heart transplants in men cumulatively (DiD = 0.956), compared with 10.23 more transplants in women cumulatively (DiD = 0.090); this sex DiD difference was not significant (P = .749). Heart transplant volumes were significantly different for both men and women across ME and non-ME states (P < .001 for both). Since 2014, ME yielded 25.67 more transplants in Whites (DiD = 0.079), 55.78 more transplants in Blacks (DiD = 0.510), 2.85 fewer transplants in Hispanics (DiD = -0.038), 37.33 more transplants in Asians (DiD = 0.316), 14.5 fewer transplants in Native Americans (DiD = -0.105), 17.38 fewer transplants in Pacific Islanders (DiD = -0.131), and 12.85 more transplants in multiracial individuals (DiD = 0.134); these ethnic DiD differences were not significant (P = .957).

Heart transplant volume is no longer skewed toward patients with private insurance, suggesting expanding public insurance increased access to heart transplantation, according to the Organ Procurement and Transplantation Network database. Through a national DiD model, ME increased heart transplant volume for Medicaid beneficiaries, largely through male, Black, and Asian patients. These benefits were dissimilar across demographic characteristics and do not benefit all groups, suggesting ME should be remodeled if the policy aim is to equitably increase volume across sexes and ethnicities.