Sunday, February 6, 2011

Nonsimultaneous kidney exchange chains produce more transplants than simultaneous chains

That's the conclusion of a new paper,
Ashlagi, Itai, Duncan S. Gilchrist, Alvin E. Roth, and Michael A. Rees, ''Nonsimultaneous Chains and Dominos in Kidney Paired Donation -- Revisited,'' American Journal of Transplantation, forthcoming, 2011.

The "revisited" in the title comes from the fact that the reverse conclusion was reached by an earlier paper in the same journal, due to a modeling error that unnecessarily constrained the length of non-simultaneous chains to be the same as simultaneous chains. (In practice, one of the main attractions of non-simultaneous chains is that they can be longer than chains in which all surgeries are performed simultaneously, since it is no longer necessary to have a different surgical team and operating room for each surgery.)

Here's the abstract of the paper:
"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."

One of the most exciting recent events in kidney exchange has been the revolution in using chains of transplants, inaugurated by Mike Rees and the Alliance for Paired Donation, which has really taken off since the publication in 2009 of the account of his first non-simultaneous extended altruistic donor (NEAD) chain:
Rees, Michael A., Jonathan E. Kopke, Ronald P. Pelletier, Dorry L. Segev, Matthew E. Rutter, Alfredo J. Fabrega, Jeffrey Rogers, Oleh G. Pankewycz, Janet Hiller, Alvin E. Roth, Tuomas Sandholm, Utku Ünver, and Robert A. Montgomery, “A Non-Simultaneous Extended Altruistic Donor Chain,” New England Journal of Medicine, 360;11, March 12, 2009 

The new paper helps explain why this new kidney exchange technology has caught on so quickly.

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