Which statement best explains why Type O blood is considered the universal donor?

• A. Type O lacks A and B antigens
• B. Type O has AB antigens
• C. Type O lacks Rh antigen
• D. Type O expresses both A and B antigens

Answer: (A)

Universal donor status in the ABO system comes from the absence of A and B antigens on the donor’s red blood cells. When a person with any ABO type receives red cells from someone who lacks A and B antigens, there are no A or B structures on the donor cells for the recipient’s anti-A or anti-B antibodies to attack. That minimizes ABO incompatibility risk during transfusion. Note that the Rh factor is a separate consideration, so the statement focused on A and B antigens correctly explains why type O blood can be given to recipients of any ABO type. In practice, for complete compatibility, the Rh status is also matched, and using packed RBCs avoids introducing donor plasma antibodies.