Burden of excess mortality after implementation of the new kidney allocation system may be borne disproportionately by middle-aged recipients.

Under the new kidney allocation system (KAS), implemented in 2014, the distribution of the best quality donor kidney grafts shifted between age groups, but it is unclear whether this change translates to meaningful differences in post-transplant outcomes. We conducted a retrospective cohort study of 20,345 deceased donor kidney transplant recipients before and 4,605 recipients after implementation of the KAS using data from the United Network of Organ Sharing. Overall, two-year mortality was greater among recipients in the post-KAS era compared with the pre-KAS era (6.31% vs 5.91% respectively, [p = 0.01]), and two-year graft loss was not significantly different between eras (9.95% and 9.65%, respectively [p = 0.13]). In analysis stratified by age group (18-45, 46-55, 56-65, and ≥66 years), relative risk of mortality was 1.48 (95% confidence interval [CI] 1.09-1.98) among recipients 46-55 years old and 1.47 (95% CI 1.18-1.81) among recipients 56-65 years old. Relative risk of all-cause graft loss was 1.43 (95% CI 1.20-1.70) among recipients 56-65 years old. There were no significant differences in relative risk of mortality or graft loss associated with the KAS era among other age groups. After adjustment for recipient characteristics and characteristics of the changing donor pool, relative risk of two-year mortality and graft loss associated with the post-KAS era was attenuated for recipients aged 46-55 and 56-65 years, but remained statistically significant. In this early analysis after implementation of the KAS, there is suggestion that increased risk of mortality and graft loss may be disproportionately borne by middle-aged recipients, which is only partially accounted for by changes in recipient and donor characteristics. These findings signal a need to continue to monitor the effects of the KAS to ensure that allocation practices both maximize utility of the kidney graft pool and respect fairness between age groups.