Explanation:
AB positive (AB+) and O negative (O-) are considered universal blood types. People who are AB+ are universal recipients, meaning they can safely receive a blood transfusion using any other blood type.1 O- individuals are universal donors, meaning their blood can be given to people of any blood type.
If you have blood type A, you have an A antigen.
If you have blood type B, you have a B antigen.
If you have an AB blood type, you have both A and B antigens. Since a person has all of the antigens that are possible, this blood type is the rarest.
If you have type O blood, you have no antigens. O negative blood is considered the universal blood donor type because it is compatible with type A, AB, B, and O positive blood.