A system whereby different types of blood are classified according to the presence or absence of antigens on the red blood cells. Understanding a patient's blood group is important in pregnancy to prevent rhesus disease, and in blood transfusion therapy. There are over fourteen different types of blood grouping methods, the most common of which is the ABO method. The ABO blood group is identified by the presence of two different types of antigens (labeled A and B) on the surface of the red blood cell. Using this method, four different types of blood classification is possible: A for Type A antigens, B for Type B antigens, AB if both are present, and O if neither are present. The plasma of patients with Type-O blood contains the antibodies anti-A and anti-B agglutinins. Patients with Type-A blood do not have the anti-A agglutinins, and those with Type-B blood have an absense of anti-B agglutinins in the plasma. Blood grouping also notes the rhesus factor in the blood. See also Rhesus Factor, rh-negative and rh-sensitivity.
