The heart transplant allocation change attenuates but does not eliminate blood group O waitlist outcome disadvantage

Patients with blood group O have historically been disadvantaged in the United Network for Organ Sharing (UNOS) heart transplant allocation system. We sought to determine whether the new UNOS allocation system implemented in 2018 had an impact on waitlist and post-transplant outcomes among blood groups.

Using the UNOS database we included all adult patients listed and transplanted with first-time single-organ heart transplant between 10/17/15 and 10/1/21. For post-transplant outcomes, we separately evaluated all adult patients transplanted with the same time-frame. We used exclusion criteria and censoring to limit biases from changing clinical practices around the allocation change (10/18/2018), and from unequal or inadequate follow-up. We compared clinical characteristics and outcomes before and after the allocation change among each blood group. Fine-Gray and Cox regression models were used to estimate the effect of the new allocation system on competing waitlist outcomes- transplantation, death-or-removal from waitlist- and post-transplant survival, respectively.

Of the 21,565 patients listed for transplantation 14,000 met criteria for waitlist analysis (7,035 in the old system vs. 6,965 in the new), and 7,657 met criteria for post-transplant analysis (3,519 in the old system vs. 4,138 in the new). Among each blood group, new allocation change was associated with higher transplantation rates lower waitlist days and lower waitlist mortality (except Group AB). However, despite improvements, Group O was still associated with worse waitlist outcomes for each metric compared to non-O Groups. The new allocation system did not have a significant impact on post-transplant survival among any blood groups.

Changes in heart transplant allocation have attenuated but not eliminated blood group O disadvantage in access to donor hearts.