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How can previous blood transfusions affect transplant tissue matching?

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Kidney transplant — transplant British surgeon Andrew Ready flushing a donated kidney during a transplant at Queen Elizabeth Hospital, Birmingham, England, 2006.

Previous blood transfusions can have complex, sometimes contradictory effects on transplant tissue matching.

Historically, it was feared that transfusions would harm a recipient's prospects by sensitizing them to donor antigens. Indeed, some patients do develop HLA antibodies against a wide spectrum of the population after receiving blood, making them "highly sensitized" and significantly more difficult to match with a suitable donor. These antibodies are identified during tissue typing, where a recipient's serum is tested against donor lymphocytes; a positive crossmatch generally contraindicates a transplant.12

Conversely, clinical observations have shown that patients who received blood transfusions prior to kidney transplantation often experienced better graft outcomes than those who had not, a phenomenon known as the "blood transfusion effect". While the exact immunological mechanism remains unknown, this observation led many centers to administer transfusions before surgery. However, due to the risk of creating highly sensitized patients who become difficult to transplant, the practice of using donor-specific blood transfusions has declined.1