ORGAN ALLOCATION IN KIDNEY PAIRED DONATION WITH NEVERENDING CHAINS

Purpose: Kidney paired donation (KPD) matches a potential kidney recipient and his incompatible donor to another incompatible pair, so that the donor of each pair gives his kidney to the recipient of the other pair.  KPD cannot serve all incompatible pairs because of the reciprocal matching requirement, so we investigate modalities for relaxing the reciprocal requirement.

 

Methods:  We compared KPD with two recently proposed modalities for relaxing the reciprocal requirement.  Domino paired donation (DPD) starts with a non-directed donor and ends with the donor of the last pair giving to the recipient at the top of the deceased donor waiting list.  Neverending chains are similar to DPD, except that the intended donor of the last donor / recipient pair becomes a bridge donor for a later transplant.  We simulated pools of incompatible donor/recipient pairs joining a national registry over two years, according to a clinically detailed model previously described (Gentry et al, Am J Transp 2006).  An integer program selected the best matching for each fixed pool of recipients and donors.  For non-simultaneous neverending chains, we tried various heuristics to ensure that the bridge donor would be likely to match in a future pool.  

 

Results:  DPD would more than double the number of transplants facilitated by each non-directed donor.  However, including neverending chains in paired donation registries would only slightly increase the proportion of incompatible donor / recipient pairs that match for a transplant, from 68.0% matched with DPD to 71.4% matched with neverending chains, if 20 incompatible pairs and 2 non-directed donors join each month.  Additionally, bridge donors will be unmatched for an average of 4.88 matching cycles before a suitable recipient is found.  Heuristic strategies of penalizing or disallowing hard-to-match AB-type bridge donors did not increase the utility of neverending chains.

 

Conclusions: Neverending chains are controversial, both because a donor who has pledged to donate on a future date may renege, and because the scheme sequesters all benefit from non-directed donors within the population of people who have a living donor available.  The utility of neverending chains is limited because the blood-type distribution advantage of a non-directed donor is lost at the first bridge donor, and because as neverending chains accumulate they compete with each other for matches within the pool.