Nonsimultaneous Chains and Dominos in Kidney Paired Donation—Revisited

Since 2008 kidney exchange in America has grown in part from the incorporation of non-directed donors in transplant chains rather than simple exchanges. It is controversial whether these chains should be performed simultaneously ("domino paired donation," DPD) or nonsimultaneously ("nonsimultaneous extended altruistic donor chains," NEAD). NEAD chains create "bridge donors" whose incompatible recipients receive kidneys before the bridge donor donates, and so risk reneging by bridge donors, but offer the opportunity to create more transplants by overcoming logistical barriers inherent in simultaneous chains. Gentry et al. simulated whether DPD or NEAD chains would produce more transplants when chain segment length was limited to three transplants and reported that DPD performed at least as well as NEAD chains. As this contrasts with the experience of several groups involved in kidney paired donation, we performed simulations that allowed for longer chain segments and used actual patient data from the Alliance for Paired Donation. When chain segments of 4-6 are allowed in the simulations, NEAD chains produce more transplants than DPD. Our simulations showed not only more transplants as chain length increased, but also that NEAD chains produced more transplants for highly sensitized and blood type O recipients