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.