Does a changing donor pool explain the recent rise in the United States kidney nonuse rate?

The proportion of deceased donor kidneys recovered for transplantation that are not transplanted reached 28% in 2023. Past research demonstrated that >90% of the nonuse rate (NUR) increase in the 2000s could be explained by the broadening donor pool. We used the Organ Procurement and Transplantation Network data to study kidneys recovered from 2010-2023, applying causal inference methods to assess the degree to which the recent, sharp rise in the NUR could be explained by changes in donor clinical characteristics. Unadjusted odds of kidney nonuse were 63% higher (95% CI: 56%, 70%) in 2023 vs 2018. After adjusting for donor factors, the odds of nonuse were only 12% (9%, 15%) higher in 2023. Both regression and propensity weighting demonstrated that 75% to 80% of the recent NUR increase can be explained by a rapidly expanding donor pool. Encouragingly, the NUR has not increased and remains low for above-average quality kidneys. However, the unexplained risk of nonuse for kidneys in the highest kidney donor risk index quartile increased by ∼ 30%, potentially due to residual confounding and/or system-level, exogenous factors such as allocation policy changes. To improve placement efficiency, allocation policy should adapt to the increasingly heterogeneous donor pool by allocating kidneys differently along the donor quality spectrum.