Why do plasma transfusions have different ABO compatibility rules than red blood cell transfusions?

The difference in ABO compatibility rules for red blood cell (RBC) transfusions versus plasma transfusions arises from the specific components being transferred and the presence of antigens or antibodies within them.12

• Red Blood Cell Transfusions: Compatibility is determined by the antigens present on the surface of the donor's red cells. If a recipient has antibodies in their serum that match the donor's antigens, it can trigger a dangerous hemolytic reaction. For example, a person with type A blood has anti-B antibodies; therefore, they cannot receive type B red cells.13
• Plasma Transfusions: Compatibility is determined by the antibodies present in the donor's plasma. Plasma contains the liquid portion of the blood, which carries antibodies against the antigens the donor lacks. Consequently, the rules are essentially reversed: a donor who is type AB is considered a universal plasma donor because their plasma lacks both anti-A and anti-B antibodies, whereas a type O donor's plasma contains both, limiting its compatibility.123

In short, RBC compatibility focuses on avoiding the recipient's antibodies attacking donor cells, while plasma compatibility focuses on avoiding donor antibodies attacking recipient cells.13