A system of classification of blood types which is based the kinds of proteins present on the surface of the red blood cell. In the ABO system there are four possible blood groups - A, B, AB, and O. Each group has an antibody in the plasma that corresponds to the antigen that is missing from the red blood cells, as seen in the following table:
If two types of blood are mixed and their antigens and antibodies clash a blood transfusion will be unsuccessful. Blood group AB is called the universal receiver as it has no A or B antibodies and can receive at a blood transfusion blood of any group; blood group O is known as the universal donor as it has neither A nor B antigens and can be given to any blood group.
Apart from their use in matching blood for transfusions, blood groups can be used to test paternity suits and for genetic studies as the presence or absence of the two antigens is hereditary. For example, two parents who have blood group type O will also have children with the same blood type. If both parents have blood type AB, their children may be of type A, B or AB.
