Continuous allocation score design for guaranteeing equity and reducing discards in kidney and liver transplantation - The benefits of kidney and liver transplantation should be available to all Americans, but geographic variation in supply and demand of organs, 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 region 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 consequences requires simulation optimization methods. These methods will maximize the survival benefit of transplantation while ensuring allocation based on medical need by making transplant rates similar for patients of equivalent medical need across geographic region, sex, ABO blood group, and immune sensitization. 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, minimizes waitlist deaths and maximizes life-years gained from transplant, while assuring transplant rates for relevant subgroups (e.g. by age, sex, 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 sexes, age groups, sensitization levels, etc.) closer to 1. We will aim to ensure similar transplant rates for candidates of equivalent medical need. 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. 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 explore waitlist outcomes in clinically detailed simulations of organ allocation. In this era of continuous allocation, we can achieve more transplants that ever before, while assuring allocation priority according to medical need.
