A blood type (also known as a blood group) is a blood classification based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). A blood group system, such as the Rh or ABO system, is made up of a group of related blood types. The prevalence of the ABO and Rh blood types varies by population.
- Blood Type A – If the red blood cell has only “A” molecules on it.
- Blood Type B – If the red blood cell has only “B” molecules on it.
- Blood Type AB – If the red blood cell has a mixture of both “A” and “B” molecules.
- Blood Type O – If the red blood cell has neither “A” or “B” molecule.
When a blood transfusion is required, blood types are critical. A patient receiving a blood transfusion must receive a blood type that is compatible with his or her own blood type. If the blood types are incompatible, red blood cells clump together and form clots, which can block blood vessels and cause death.
When two different blood types are mixed together, the blood cells may begin to clump together in the blood vessels, potentially resulting in a fatal situation. As a result, blood types must be matched before blood transfusions can take place. Type O blood can be given in an emergency because it is most likely to be accepted by all blood types. There is, however, a risk involved.