Why do doctors have to check what blood type a person has before receiving a transfusion?
A. Different blood types have different antibodies that will be attacked by someone with antigens against that blood type.
B. Different blood types have different antigens that will be attacked by someone with antibodies against that blood type.
C. They need to have the same blood type because their DNA must be similar enough to blend or will cause side-effects and possibly be rejected.
D. Your blood type doesn't matter as long as you get the correct amount of blood in a transfusion.

Doctors need to check the blood type of a person before administering blood transfusion because different blood types have different antibodies that will be attacked by someone with antigens against that blood type.

The blood that would be given to a person must match the blood of that person in terms of the type of antigens. If the blood antigens are different, the antigens present in the blood of the individual undergoing blood transfusion would consider the antigens present in the blood being received as an enemy and attack it. This will lead to agglutination of the blood in the system of the person, a process that often leads to death.

Hence, O-positive individuals must always receive O-positive blood while O-negative individuals must always receive O-negative blood.

The correct options are A and B.