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) liv ing donors and their recipients. One variation that has greater potential e xchanges living donor kidneys for cadaveric donor kidneys (indirect exchang es). A primary concern with indirect exchanges is the potential to disadvan tage blood group O wait list candidates. Using wait list modeling, we exami ne whether this proposal would disadvantage cadaveric kidney blood group O wait list candidates, and present an approach for neutralizing these negati ve effects. Methods. A probability model estimated the total number and blood type freq uencies of donor-recipient pairs that would participate in indirect exchang es. A supply-to-demand model for the cadaveric kidney wait list estimated t he mean wait time under different al. location policies and donor selection mechanisms for candidates on the wait list classified according to the can didates' race and blood type. Results. Indirect exchanges will reduce the mean wait time for cadaveric ki dney wait list candidates. The mean wait time of blood group O cadaveric ki dney wait list candidates increases when the participating living donors se lf-select and when kidney allocation is determined by efficiency. This is n eutralized when the transplant team preferentially selects blood group O li ving 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 gr oup O candidates will not be affected adversely if blood group O living don ors are selected preferentially and if allocation is based on need.