Primum non nocere: Avoiding harm to vulnerable wait list candidates in an indirect kidney exchange

Background. One proposal to increase kidney transplantation is to exchange kidneys between pairs of ABO-incompatible (or cross-match-incompatible) living donors and their recipients. One variation that has greater potential exchanges living donor kidneys for cadaveric donor kidneys (indirect exchanges). A primary concern with indirect exchanges is the potential to disadvantage blood group O wait list candidates. Using wait list modeling, we examine whether this proposal would disadvantage cadaveric kidney blood group O wait list candidates, and present an approach for neutralizing these negative effects. Methods. A probability model estimated the total number and blood type frequencies of donor-recipient pairs that would participate in indirect exchanges. A supply-to-demand model for the cadaveric kidney wait list estimated the mean wait time under different al. location policies and donor selection mechanisms for candidates on the wait list classified according to the candidates' race and blood type. Results. Indirect exchanges will reduce the mean wait time for cadaveric kidney wait list candidates. The mean wait time of blood group O cadaveric kidney wait list candidates increases when the participating living donors self-select and when kidney allocation is determined by efficiency. This is neutralized when the transplant team preferentially selects blood group O living donors and cadaveric kidney allocation is determined by need. Conclusion. Indirect exchange programs will significantly shorten the wait times for cadaveric kidney wait list candidates. The wait times of blood group O candidates will not be affected adversely if blood group O living donors are selected preferentially and if allocation is based on need.