Kidney paired donation / exchange

Kidney paired donation (KPD), also called kidney paired exchange or kidney exchange, is a living-donation strategy that allows a candidate who has a willing but medically incompatible living donor to receive a compatible kidney by "swapping" donors with one or more other incompatible donor-recipient pairs.[1][2] In the simplest case, two incompatible pairs are matched so that the donor of the first pair gives to the recipient of the second pair and vice versa; longer cyclic exchanges and donor "chains" initiated by a non-directed (altruistic) donor extend the same idea to three, four, or many more pairs.[1][3] In the United States, KPD is run through the national OPTN Kidney Paired Donation Pilot Program (KPDPP) and through several independent nonprofit registries.[1][4]

KPD does not create new donors; it re-routes the kidneys of people who are already willing to donate, so that biological incompatibility no longer blocks a transplant. It is now a major source of living-donor kidney transplants: paired-donation transplants reached 1,346 in 2024, about 21.3 percent of living-donor kidney transplants in the United States, more than double the 10.4 percent share of 2014.[5]

The problem it solves

Roughly a third of would-be living kidney donors are incompatible with their intended recipient.[2] The two principal barriers are ABO blood-group incompatibility (for example, a type-A donor and a type-O recipient) and HLA incompatibility, in which the recipient carries preformed antibodies against the donor's human leukocyte antigens that would cause a positive crossmatch and hyperacute rejection.[2][6] Highly sensitized candidates, quantified by a high calculated panel-reactive antibody value, have antibodies against a large fraction of the donor population and are the hardest to match (see Panel-reactive antibody, cPRA and sensitization).[6] KPD lets such a pair trade its donor for a compatible one rather than abandoning living donation or attempting desensitization.[2][6]

Basic mechanics

KPD arrangements take several forms:[1][3][7]

• Two-way exchange (swap). Two incompatible pairs exchange donors so that each recipient receives a compatible kidney. The two donor operations are normally performed simultaneously.
• Three-way and longer cyclic exchanges. Three or more pairs are arranged in a closed cycle (pair A's donor gives to B's recipient, B's donor to C's recipient, C's donor back to A's recipient). Larger cycles let optimization software match harder pairs, but a closed cycle classically requires all operations at once, which is logistically demanding.
• Non-directed-donor (altruistic) chains. A non-directed donor (someone donating a kidney to a stranger) gives to the recipient of an incompatible pair; that pair's own donor then "pays it forward" to the next pair, and so on. A chain ends with a kidney directed to a candidate on the deceased-donor waiting list.
• Non-simultaneous, extended, altruistic-donor (NEAD) chains. Because chains need not close back on themselves, the operations can be staggered in time. The last donor in a completed segment becomes a bridge donor who continues the chain weeks or months later. This relaxes the all-at-once constraint and, if a bridge donor withdraws, no recipient who already donated is left without a kidney. The concept was demonstrated in a 10-transplant chain reported in 2009, in which bridge donors continued the chain up to five months after their own paired recipients had been transplanted.[3]

Matching and logistics

Pairs are entered into a registry, where periodic optimization algorithms search for two-way swaps, longer cycles, and chains that maximize the number (and, in weighted schemes, the difficulty) of transplants achievable across the pool.[1][7][8] The mathematics of kidney exchange has been an active research area, and several Nobel-recognized economists contributed to the matching theory underlying it.[3][7]

A central logistical question is simultaneous versus non-simultaneous surgery. Closed cycles are typically done simultaneously so that no donor gives a kidney before "their" recipient is transplanted; open chains can be non-simultaneous because a bridge donor's later donation does not retroactively disadvantage an already-transplanted recipient.[3][7] To avoid sending donors and recipients across the country, many programs ship the recovered kidney between centers rather than having the donor travel; studies of cold-ischemia time in shipped paired-donation kidneys have supported this practice.[8]

United States programs

KPD in the United States is carried out through both the national program and independent registries:[1][4][9]

• OPTN Kidney Paired Donation Pilot Program (KPDPP). Operated by the United Network for Organ Sharing (UNOS) under the federal OPTN contract, the national program ran its first computerized match in October 2010 and is open to OPTN-approved living-donor kidney programs.[4][9]
• Independent nonprofit registries. Several nonprofit organizations operate their own multi-center exchange pools, among them the National Kidney Registry (NKR) and the Alliance for Paired Kidney Donation (APD). These registries match large pools of pairs and have facilitated long altruistic-donor chains; they are described here only as nonprofit facilitators, without endorsement of any particular program.[1][3]

Compatible-pair participation and desensitization alternatives

Some compatible pairs choose to enter KPD anyway, for example to obtain a younger, lower-KDPI-equivalent kidney or a better HLA match while their original donation seeds a chain that benefits a harder-to-match candidate; the trade-offs of compatible-pair participation are debated in the literature.[2][7] The principal alternative to KPD for an incompatible pair is desensitization, using plasmapheresis, intravenous immunoglobulin, and other therapies to lower the recipient's antibody levels enough to permit transplant across the barrier. Desensitization is costly, carries higher rejection risk, and is generally reserved for candidates who cannot be matched through exchange.[2][6]

Outcomes and ethics

KPD expands access to living-donor kidneys, which on average outlast deceased-donor kidneys, for incompatible and sensitized candidates, and chains seeded by a single altruistic donor can yield many transplants.[2][3] Its central ethical and legal feature is financial neutrality: no money or other valuable consideration changes hands, only kidneys. Because the National Organ Transplant Act (NOTA) makes it unlawful to transfer a human organ for "valuable consideration," there had been legal uncertainty over whether the reciprocal nature of an exchange ran afoul of that prohibition.[10][11] Congress resolved the question with the Charlie W. Norwood Living Organ Donation Act of 2007 (Pub. L. 110-144, enacted December 2007), which amended NOTA to clarify that "human organ paired donation" does not constitute the transfer of valuable consideration, so long as the participating pairs enter a single agreement to donate and receive on the basis of biological compatibility.[10][11] See also Financial neutrality.

Epidemiology

In 2024, paired-donation kidney transplants numbered 1,346 in the United States, roughly 21.3 percent of living-donor kidney transplants, up from about 10.4 percent in 2014; the 2023 share was about 20.6 percent.[5] These point-in-time figures come from the OPTN/SRTR Annual Data Report and should be re-confirmed against the registry at publication.

See also

• Living donation
• Kidney transplantation
• Panel-reactive antibody, cPRA and sensitization
• National Organ Transplant Act (NOTA)
• Financial neutrality
• KDPI and KDRI / donor-quality concepts

References

• Health Resources and Services Administration / OPTN. Kidney paired donation for patients. https://optn.transplant.hrsa.gov/patients/about-donation/living-donation/kidney-paired-donation-for-patients/
• Wallis CB, Samy KP, Roth AE, Rees MA. Kidney paired donation. Nephrol Dial Transplant. 2011;26(7):2091-2099. doi:10.1093/ndt/gfr155. PMID:21555392
• Rees MA, Kopke JE, Pelletier RP, Segev DL, Rutter ME, Fabrega AJ, et al. A nonsimultaneous, extended, altruistic-donor chain. N Engl J Med. 2009;360(11):1096-1101. doi:10.1056/NEJMoa0803645. PMID:19279341
• Health Resources and Services Administration. Kidney Paired Donation Pilot Program (KPDPP). https://www.hrsa.gov/optn/patients/organ-donation/living-donation/kidney-paired-donation-pilot-program-kpdpp
• OPTN/SRTR 2024 Annual Data Report: Kidney. Am J Transplant. 2026. (Paired-donation living-donor kidney transplants: 1,346 in 2024, ~21.3% of living-donor kidney transplants; ~20.6% in 2023; ~10.4% in 2014. As of the 2024 OPTN/SRTR report.) https://srtr.hrsa.gov/adr/2024/Kidney/
• Justiz Vargas AN, et al. Transplantation Immunology. StatPearls. NBK538218. https://www.ncbi.nlm.nih.gov/books/NBK538218/
• Ashlagi I, Roth AE. Kidney exchange: an operations perspective. Manage Sci. 2021. (Reviews two-way/cyclic exchanges, chains, and matching optimization.) https://web.stanford.edu/~iashlagi/papers/NeadChains1.pdf
• Treat E, Chow EKH, Peipert JD, et al. Shipping living-donor kidneys and transplant recipient outcomes. Am J Transplant. 2018;18(3):632-641. doi:10.1111/ajt.14597. PMID:29165871
• OPTN. First kidney paired donor transplants performed in national pilot program (first national match run October 27, 2010). https://optn.transplant.hrsa.gov/news/first-kidney-paired-donor-transplants-performed-in-national-pilot-program/
• Charlie W. Norwood Living Organ Donation Act of 2007, Pub. L. 110-144 (H.R. 710, 110th Congress), enacted December 2007; amending 42 U.S.C. §274e. https://www.congress.gov/bill/110th-congress/house-bill/710
• Congressional Research Service. Living Organ Donation and Valuable Consideration. Report RL33902. https://www.everycrsreport.com/reports/RL33902.html