Blood Groups and Blood Types

Since the turn of the century blood transfusions have been used to treat individuals suffering from anemia or low blood volume. Early attempts found that individuals fall within certain blood groups such that transfusions require preliminary screening to insure compatibility between donor and recipient. Genetically established combinations of glycoproteins and glycolipids on the surface of RBCs characterize different blood groups. Blood types within certain blood groups act as antigens to one another; therefore, if an individual receives a blood transfusion from someone with an incompatible blood type, agglutination (clumping) will occur as antibodies adhere to the antigen (invader). This process is visible to the naked eye as the blood appears more granular. Antigens reside on the surface of RBCs, while antibodies reside in blood plasma. It is important to note that the transfusion process from donor to recipient filters blood plasma, thereby eliminating problems associated with antibodies from the donors blood.

As the table displays, individuals with blood type A have antibodies that target Type B RBCs. Likewise, Blood type B has antibodies that target type A RBCs. Individuals with both AB antigens cannot have either A or B antibodies, since they would attach to their own native RBCs. Therefore, AB blood type is the universal recipient. By contrast, type O has no antigens, yet has both A and B antibodies. As already noted, a donors plasma (hence, antibodies) are filtered from transfusion; therefore, type O is the universal donor, but can only receive from other type O donors.