Blood Type and Living Organ Donation

The basic ABO rules for solid organ transplant

For most solid organ transplants, ABO compatibility follows the same matrix as red cell transfusion: O can give to anyone, AB can receive from anyone, A and B can give to AB and to their own group. See our organ transplant page for the matrix and the additional matching layers (HLA tissue typing, crossmatch testing for pre-existing antibodies).

For deceased donor allocation, the ABO rule is generally observed strictly. The deceased donor pool is small, the recipient's wait time is long, and the lack of advance preparation makes ABO-incompatible deceased donor transplant impractical in most cases. The ABO rule directly affects waiting time: patients of less common blood types (B, AB) often wait longer if the local donor pool has fewer matches.

For living donor transplant, the rules have relaxed in two ways: paired exchange (matching incompatible pairs across the programme) and ABO-incompatible transplant (planned transplant across the ABO barrier).

Kidney paired exchange (KPD)

Paired exchange addresses a common scenario: a willing living donor and an intended recipient who are not compatible (ABO mismatch, HLA antibody mismatch). Rather than the donor walking away, the pair joins a register of similarly-incompatible pairs. Computer algorithms search for two-way swaps and longer chains.

The simplest version is a two-way swap: pair A's donor is compatible with pair B's recipient, and pair B's donor is compatible with pair A's recipient. Both transplants happen (typically simultaneously, to prevent one donor backing out after their recipient receives the kidney) and both recipients get a compatible organ.

Longer chains are often started by an altruistic non-directed donor (someone who gives a kidney to an unknown recipient with no expectation of return). The non-directed donor donates to pair A's recipient, pair A's donor donates to pair B's recipient, and so on. Chains of 10 or more recipients have been documented in published case series.

The UK Living Kidney Sharing Scheme (UKLKSS), the US National Kidney Registry (NKR), and the Canadian Kidney Paired Donation Program all run these matching algorithms with regular run cycles.

ABO-incompatible kidney transplant

ABO-incompatible (ABO-i) kidney transplant is the planned transplantation of a kidney across the ABO barrier. It is offered in patients where paired exchange is not available and where the recipient and donor are willing to undertake the additional preparation.

The pre-transplant preparation removes the recipient's anti-A and anti-B antibodies that would attack the donor kidney. This is done with plasmapheresis or specialised immunoadsorption columns, repeated until the antibody titre is below a threshold (typically 1:8 or 1:16 depending on the centre's protocol). Specific immunosuppression (often including rituximab or splenectomy in older protocols) prevents the immune system from rebounding rapidly after transplant.

Outcomes have improved substantially. The first generation of ABO-i kidney transplant programmes had higher rates of graft loss; modern programmes report graft survival rates comparable to ABO-compatible kidney transplant in many series. The procedure adds cost and complexity but expands the pool of suitable donors substantially.

ABO-i is most commonly used in centres without large paired exchange programmes, in patients where the donor is highly motivated and timing is critical, and in patients where the alternative is years of waiting on the deceased donor list.

Other organs: liver, heart, pancreas, lung

Living donor liver transplant is established but technically demanding. ABO-incompatible liver transplant is offered in selected adult cases and is more commonly used in paediatric liver transplant where the recipient's immune system is less developed and the response to ABO-i is more favourable. The UK NHSBT Living Liver Donation page covers the UK programme.

ABO-incompatible heart transplant is offered in selected paediatric cases (especially infants under one year of age, where natural anti-A and anti-B antibody titres are still low) and increasingly in some adult programmes for highly sensitised recipients. The 2001 Lancet report from the Toronto group on infant ABO-i heart transplant established the modern paediatric practice.

Pancreas, lung, and intestinal transplant generally require strict ABO matching. The technical and immunological complexity of these procedures plus the smaller donor pools have limited routine ABO-incompatible programmes for these organs.

The altruistic kidney donor

A non-directed (or altruistic) kidney donor gives a kidney to an unknown recipient with no expectation of return. The donor goes through full medical and psychological assessment to confirm they are healthy enough to donate and that the decision is fully informed and free of coercion. Once approved, the donor enters the system as a chain initiator for paired exchange, or donates to a deceased-donor-list patient with longest wait time and best match.

The first UK altruistic donor cases were in 2007. The UK programme has since enabled hundreds of paired-exchange chains. The US altruistic donor programme is older and has supported much larger cumulative numbers.

Living kidney donors have a small but real procedural risk (about 0.03 percent perioperative mortality, similar to other major elective surgery) and a small long-term risk of progressive renal impairment in the remaining kidney. Long-term outcomes for donors are similar to comparable healthy non-donors in published cohort studies. The decision is informed and personal; the assessment process is thorough.

The UK NHSBT living donation page and the US OrganDonor.gov have practical information on the assessment process and what to expect.

Deceased donor organ allocation and blood type

Most organ transplants come from deceased donors. The allocation of these organs follows ABO compatibility plus clinical priority criteria (medical urgency, time on waiting list, HLA matching, geographic proximity, paediatric priority). The detailed allocation algorithms are published by the relevant national transplant authority.

Patients of less common blood types (especially type B and type AB) tend to have longer waits in many regions because the local deceased donor pool reflects the population blood type distribution. The geographic variation in donor distribution (see our distribution by ethnicity page) interacts with the allocation algorithm to produce different waiting times in different regions and ethnic groups.

For UK patients, the NHSBT Organ Donation register and the deceased donor allocation system are managed centrally. For US patients, the United Network for Organ Sharing (UNOS) manages the OPTN waiting list and allocation.

Frequently asked questions

Related pages