There are four primary types of blood. These are:
- Type A: The A antigen indicates type A blood. This means the plasma in your blood will attack type B blood. About 36% of people (36 in 100) in the United States have type A blood, with 6% having A-negative (A-) blood and 30% having A-positive (A+) blood.
- Type B: The B antigen indicates type B blood, which means that the plasma in your blood will attack type A blood. About 11% of people (11 in 100) in the U.S. have type B blood, with 2% having B-negative (B-) blood and 9% having B-positive (B+) blood.
- Type O: Type O blood contains neither the A nor B antigen, meaning the plasma in your blood will attack both A and B blood. About 44% of people (44 in 100) in the U.S. have type O blood, with 7% having O-negative (O-) blood and 37% having O-positive (O+) blood.
- Type AB: This blood type contains both A and B antigens, which means your blood does not contain antibodies for either protein. About 48% of people (48 in 100) in the U.S. have type O blood, with 9% having O-negative (O-) blood and 39% having O-positive (O+) blood.
Type O negative blood does not contain any antigens. This is why O negative blood is known as the “universal donor” blood type, as the plasma in O negative blood will not attack any other blood type. Inversely, type AB positive blood is known as the “universal recipient” type.
Blood transfusions require the blood being given to be the same type as that of the recipient. So, if an individual with type B negative blood requires a blood transfusion, they must be given either O negative blood or type B negative blood. If a different blood type is transfused into the body, the plasma of the recipient’s blood will attack the new blood. This leads to a condition known as a transfusion reaction - which can lead to serious illness or death.
Incompatible blood transfusions are rare, due to the accuracy of modern blood type tests.