Blood Type Compatibility for Organ TransplantKidney, Liver, Heart - 2026 Guide
ABO blood type compatibility is the first gate in organ transplantation - but not the only one. HLA tissue typing, crossmatch testing, and organ-specific medical factors all influence whether a transplant can proceed.
ABO Compatibility Matrix for Organ Transplant
| Donor type | Can donate organ to | Compatible recipients |
|---|---|---|
| A+ | A+, AB+ | A+, A-, O+, O- |
| A- | A+, A-, AB+, AB- | A-, O- |
| B+ | B+, AB+ | B+, B-, O+, O- |
| B- | B+, B-, AB+, AB- | B-, O- |
| O+ | O+, A+, B+, AB+ | O+, O- |
| O- | O+, O-, A+, A-, B+, B-, AB+, AB- | O- |
| AB+ | AB+ | A+, A-, B+, B-, O+, O-, AB+, AB- |
| AB- | AB+, AB- | A-, B-, O-, AB- |
ABO compatibility for organ transplant follows the same rules as red-cell transfusion. However, this table represents only ABO compatibility - HLA matching, crossmatch, and sensitisation testing are required in addition.
Beyond ABO: What Makes Transplant Different from Transfusion
A blood transfusion lasts hours or days before the donated cells naturally die. An organ transplant is permanent - the organ must survive for years or decades without rejection. This durability requirement demands more stringent compatibility testing.
HLA Tissue Typing
Human Leukocyte Antigens (HLA) are proteins on virtually every cell in your body except red blood cells. Unlike ABO, HLA typing is not a single system - there are thousands of HLA variants. A closer HLA match between donor and recipient reduces the risk of chronic rejection and may allow lower immunosuppression doses. Kidney transplants particularly benefit from HLA matching; heart and liver transplants are less strictly HLA-matched due to the urgency of allocation.
Crossmatch Test
A crossmatch takes the recipient's serum and mixes it with donor cells to check for pre-formed antibodies specific to that donor. A positive crossmatch (recipient has antibodies to donor) is generally a contraindication to transplant because those antibodies would mount an immediate hyperacute rejection. Sensitisation can occur from prior transfusions, pregnancies, or previous transplants.
Panel Reactive Antibody (PRA)
PRA measures what percentage of the population a patient has pre-formed antibodies against. A patient with 80% PRA is highly sensitised - 80% of potential donors would trigger a positive crossmatch. Highly sensitised patients may wait significantly longer for a suitable match.
Kidney Transplant: Living Donors and Paired Exchange
Kidneys are the most commonly transplanted organ. Unlike heart or liver transplant (where only deceased donors are an option), a living person can donate one kidney. However, when a willing living donor is ABO-incompatible with the intended recipient, the donation cannot proceed directly.
This is where kidney paired exchange (KPE) programs come in. If Donor A is incompatible with Recipient A, but Donor B is compatible with Recipient A, and Donor A is compatible with Recipient B, the two pairs can "swap" - each recipient gets a compatible kidney from the other pair's donor.
Large paired exchange networks (coordinated by UNOS, the National Kidney Registry, and regional programs) can chain multiple swaps together - a single chain of 8-10 transplants triggered by one altruistic non-directed donor is not uncommon. According to the National Kidney Foundation, more than 3,000 paired exchange transplants were performed in the US in recent years.
Liver Transplant: ABO and Emergency Exceptions
Liver transplant primarily follows ABO compatibility rules. However, the liver has unique tolerance properties. In paediatric emergency cases, when no ABO-compatible liver is available and the child would die without transplant, an ABO-incompatible liver may be used. Young children (typically under 12 months) have not yet developed robust anti-blood-group antibodies, providing a window of partial tolerance.
In adults, ABO-incompatible liver transplants carry a significantly higher risk of rejection and are generally avoided. They may occasionally be considered in life-threatening circumstances with no compatible organ available and with plasma exchange to reduce antibody levels.
Heart Transplant: ABO Incompatibility in Infants
In adults, heart transplant requires strict ABO compatibility - incompatible hearts are rejected immediately. However, in infants under approximately 14 months of age, ABO-incompatible heart transplantation has been performed successfully. Infant immune systems have not yet developed isohemagglutinins (the antibodies against blood group antigens), giving a developmental window where ABO incompatibility can be tolerated.
This approach, pioneered at the Hospital for Sick Children in Toronto, has allowed infants who would otherwise die waiting for a same-type donor to receive hearts from a broader compatible pool. The approach does not apply to older children or adults.
How the US Organ Allocation System Works
UNOS (United Network for Organ Sharing) manages the national organ transplant waiting list through its OPTN (Organ Procurement and Transplantation Network). When a deceased donor organ becomes available, a computer algorithm ranks potential recipients based on:
- Blood type compatibility (ABO)
- HLA tissue matching score
- Crossmatch result
- Medical urgency (status)
- Time on the waiting list
- Geographic proximity (organ viability decreases with transport time)
- Body size match (particularly for heart and lung)
- Sensitisation level (PRA score)
Source: UNOS/OPTN