PROJECT ABSTRACT
The benefits of kidney and liver transplantation should be available to all Americans, but geographic,
racial/ethnic, gender, and other disparities, plus a shortage of transplantable organs, have frustrated that
promise. Because organ allocation is a complex system in which every factor prioritized affects how other
factors are prioritized, policy changes that focus on one aspect (e.g. geographic disparity or panel reactive
antibody) in isolation often fail. Prior allocation changes have often resulted in unintended consequences. The
Organ Procurement and Transplantation Network (OPTN) has resolved to eliminate geographic boundaries in
favor of continuous allocation through implementation of a composite allocation score (CAS). However,
eliminating geographic boundaries impacts the rest of the system. To design a CAS for continuous allocation
that retains priorities of the current system without introducing unintended disparities requires simulation
optimization methods. These methods will maximize the survival benefit of transplantation while ensuring
equity by making transplant rates similar among populations that differ by race, gender, and social
determinants of health. To address the challenge of kidney and liver continuous allocation, we propose to
efficiently apply simulation and explore a vast number of alternative designs to choose a CAS that eliminates
geographic boundaries, as per the OPTN mandate, without inducing unintended new disparities. This system
will minimize waitlist deaths and maximize life-years gained from transplant, while assuring transplant rates for
relevant subgroups (e.g. by age, race, ABO blood type, urban/rural) comparable to the current system. We
then propose to improve on the CAS by making incidence rate ratios (the relative transplant rates between
races, genders, sensitization levels, etc.) closer to 1. Whether perfect equity along all these dimensions can be
achieved is an open question, but we will attempt to equalize access for every candidate. Finally, we will
explore ways the CAS might minimize discard of transplantable organs. We will use previously unavailable
timestamp data on organ offers to create a logistics and discard simulation that will predict how allocation
changes impact cold ischemia time and discards for the first time. Using this new tool, we will test prioritizing
offers to centers and candidates most likely to accept them, while maintaining equity of access. The score can
adapt flexibly as transplant center acceptance criteria change. Our findings will be immediately and directly
applicable to national conversations regarding kidney and liver allocation, using an approach that optimizes
outcomes and supports transparency, an ethical cornerstone in transplantation. Our methodology allows
stakeholders to enforce constraints on equity and outcomes in clinically detailed simulations of organ
allocation. In this era of continuous allocation, we can achieve more transplants–and assure they are more
equitably distributed–than ever before.
