Association Between Donor-recipient Matchability, Access to Transplantation, and Posttransplant Outcomes.

Background: Globally, deceased donor kidney allocation algorithms prioritize HLA matching, potentially disadvantaging transplant candidates with less common HLA alleles. This study developed an Australian Matchability score (M-score) to assess access to transplantation and posttransplant outcomes based on HLA match probability. Methods: M-scores were calculated by comparing all recipients and donors with complete HLA-A, HLA-B, and HLA-DR data from the Australia and New Zealand Dialysis and Transplant Registry (July 1, 2006-December 31, 2023). Multivariable Cox regression was used to analyze associations between M-score quartiles and time to transplantation as well as transplantation outcomes. Results: HLA data from 14 836 recipients and 7708 donors were used to generate M-scores. Of these, 10 760 recipients had available waitlist data and were included in the models. M-scores were normally distributed with a mean ± SD of 11.4 ± 0.9. The proportion of non-European Australians increased significantly with each quartile (ie, more difficult to HLA match), Q1: 16%, Q2: 26%, Q3: 40% Q4: 60% (P < 0.001). Compared with Q1, patients in Q4 were significantly less likely to receive a deceased donor kidney transplant (adjusted hazard ratio [aHR] 0.56; 95% confidence interval [CI], 0.52-0.60; P < 0.001) had the highest risk of death-censored graft loss (aHR 1.39; 95% CI, 1.01-1.91; P = 0.05) and acute rejection (aHR, 1.29; 95% CI, 1.09-1.52; P = 0.002). Conclusions: The M-score identifies transplant recipients with difficult-to-match HLA profiles. Higher M-scores were associated with a lower likelihood of transplantation and an increased risk of death-censored graft loss and acute rejection. These findings highlight significant inequities in the current HLA-based algorithm for deceased donor allocation.