What is kidney paired donor exchange?
Barriers against living kidney donation include ABO blood group incompatibility and existence of preexisting HLA antibodies between potential donor-recipient pairs. In a Kidney Paired Donor Exchange (KPDE) program, a medically approved incompatible pair is able to receive and exchange with other incompatible pair(s). This results in compatible organs for all recipients. The first KPDE was established in the United States in 2000. There were a total of 552 kidneys transplanted in 2014 with the KPDE program, amounting to about 10% of all living donor transplants that year.
The five different types of exchange include:
1. Two-way is between two incompatible pairs with the procurement operations occurring simultaneously so that neither donor could back out.
2. k -Way ( k is the number of pairs) is exchanges between more than two pairs using the same concept of the two-way exchange. Reciprocally matching donors are not required. For example, Pairs A, B, and C, Pair A donor is compatible with Pair B recipient, but Pair B donor is not a match for the Pair A recipient. However, Pair C donor is a match for Pair A recipient and Pair C recipient is a match for Pair B donor. Now all three recipients receive a transplant from a compatible donor. Due to logistical reasons of the donors required to be in the operating room at the same time, the number in this exchange is usually limited to 3 to 4 pairs.
3. Unspecified donor chain starts with an unspecified donor (altruistic donor), who, instead of, as previously, donating to the deceased donor list, would now donate to an incompatible pair. The donor in this incompatible pair would donate to another incompatible pair and this pattern would continue, forming a chain. The last donor in the chain would donate to the deceased donor list, ending the chain. This modality of donor exchange is called the domino-paired donation (DPD). Since it is possible to arrange these chains so that no donor-recipient pair had to donate a kidney before receiving a kidney, the requirement for all donors to be in the operating room simultaneously was relaxed. This allowed for the development of the non-simultaneous extended altruistic donor chains. The last donor in a DPD would become a “bridge” donor, which meant instead of donating to the deceased donor list, the donor would donate to another incompatible pair at a later time, thus extending the chain.
4. List exchange is when a donor in an incompatible pair donates to the deceased donor list and their recipient is now given priority for a deceased donor organ transplant.
5. Altruistically unbalanced exchange is between a compatible pair and another incompatible pair. It allows an incompatible pair to find a donor and affords the opportunity for the compatible pair to receive a kidney of higher quality.