KDPI-dependent ranking policies : shaping the allocation of deceased-donor kidneys in the new era

The deceased-donor kidney transplant candidates in the US are ranked according to characteristics of both the donor and the recipient. We seek the ranking policy that optimizes the efficiency-equity tradeoff among all such policies, taking into account patients' strategic choices. Our approach considers a broad class of ranking policies, which provides approximations to the previously and currently used policies in practice. It also subsumes other policies proposed in the literature previously. As such it facilitates a unified way of characterizing good policies. We use a fluid model to approximate the transplant waitlist. Modeling patients as rational decision makers, we compute the resulting equilibria under a broad class of ranking policies, namely the achievable region. We then develop an algorithm that optimizes the system performance over the achievable region. We show analytically that it suffices to restrict attention to priority scores that are affine in the patient's waiting time. We also show through a numerical study that the total QALYs can be increased substantially by allowing patient rankings to depend on the kidney quality. Lastly, we observe that there is almost no improvement if only the healthier patients are prioritized for certain kidney types. Our results verify that ranking patients differently for kidneys of different quality can reduce the survival mismatch and the kidney wastage significantly. Consequently, the policy change in 2014, that implemented prioritizing the healthiest patients when allocating the highest 20% quality organs, is a step in the right direction. For further improvement, one may consider revising the current policy by also prioritizing the least healthy patients on the waitlist for the lowest-quality organs