Why O is the universal donor?

Answer 1

The different blood types are A, B, AB and O. The interaction of these different types depends on two factors: (1) the antigen expressed on the surface of the RBC and (2) that antibody produced in the blood. The antibody in a certain blood type can cross-react with the antigen of another blood type and result in a medical emergency for the recipient if they are not properly matched. The antibody-antigen interaction can result in activation of the complement system and intravascular hemolysis.

Type A blood produces "A" antigen and "anti-B" antibodies.

Type B blood produces "B" antigen and "anti-A" antibodies.

Type AB blood produces both "A" and "B" antigen but no antibodies.

Type O blood produces no antigen but both "anti-A" and "anti-B" antibodies.

If a person with type A blood received a transfusion with type B blood, the recipient's "anti-B" antibodies would attack the B blood cells. However, if the same person received type O blood, the "anti-B" antibodies have no target antigen and thus would not attack the O blood cells. This is also true for B blood type recipients.

Note: the "anti-A" and "anti-B" antibodies from the O donor, after diluted in the recipient's blood, do not mount a sufficient immune response to cause a concern in most cases. Also, often "packed blood cells" are given with the plasma removed, which contains the largest concentration of the antibodies.

Thus, because O blood type does not express any antigen on it's surface that can serve as a target for antibodies produced by the recipient, it is considered the universal donor.

Type O can be given to anyone no matter their blood type. O- is best but it is very rare. It has neither antibody for A, b or AB and so it will not cause agglutination.

Because it does not contain any "A" or "B" proteins. "O"- Negative would not contain the rhesus "Rh" factor either, further making it the universal donor.

Answer 2

O negative (O-) is the universal blood donor because it does not have either the A or the B antigens found in other blood cells, which makes it safe for transfusion.

However O- and O+ can only receive blood from the same blood group, due to the lack of the A and B antigens.