An antigen is a substance on red blood cells. These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, and they determine your blood type. The four main blood types are A, B, O and AB. There are more than 600 known antigens, and some are unique to specific racial and ethnic groups. For example, many African Americans and people of African descent have rare blood types, such as types U negative and Duffy negative.
Additionally, about half of African Americans have type O positive blood, which is the most transfused blood type in the United States. Type O positive blood is one of the first types to run out during a shortage due to high demand, which is why O positive donors of all backgrounds are always needed to maintain a healthy blood supply.
Some patients require an even closer blood type match than the main blood types. In fact, a person with sickle cell disease may need a precise pairing with a blood donor, especially if frequent transfusions are necessary. If a patient receives a transfusion of a blood type that is not an exact match, they will form antibodies against the mismatched antigens. If the patient receives another transfusion that contains those same antigens in the future, the ensuing complications could lead to death.