What residual risk remains when type O blood is given to a type A recipient?

1. Type O erythrocytes carry no A or B antigen, so the recipient anti-B antibodies find nothing to attack. 2. That takes care of the donated cells, which is why type O is usable in an emergency. 3. But type O plasma always carries both anti-A and anti-B antibodies. 4. Transfusing it into a type A recipient therefore introduces anti-A antibodies directed at the recipient own erythrocytes. 5. The adverse effect is typically limited because the transfused volume is much smaller than the volume of the recipient own blood. 6. The risk is real but diluted, so the answer is the incoming plasma antibodies rather than an immediate attack on the donor cells. 7. Blood group antigens are genetically determined and fixed, so no recipient starts making new A antigens in response to a transfusion. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.6 Blood Typing_