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Why do ABO blood groups matter in organ transplantation?

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Close-up illustration of multiple human red blood cells with their characteristic disc shape, floating against a red background. — blood group The major component of human blood is the red blood cell.

ABO blood groups are critical in organ transplantation because the ABO antigens are not restricted to red blood cells; they are widely distributed throughout the tissues of the body.1

When an organ is transplanted, the recipient's immune system uses these antigens to distinguish between "self" and "nonself" substances. If a donor organ carries ABO antigens that are incompatible with the recipient's blood type, the recipient's pre-existing antibodies can recognize the donor tissue as foreign. This often triggers a rapid and severe rejection response that can occur within minutes or hours and is generally irreversible.23

Because of this risk, surgeons typically prioritize matching the donor and recipient according to the ABO blood group system to ensure the graft is accepted. While novel techniques such as desensitization therapy—which filters out harmful antibodies from the patient's blood—now allow for some ABO-incompatible transplants, matching remains a fundamental standard in clinical practice to prevent immune-mediated damage to the donor organ.14