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The leading cause of death from hemolytic transfusion reactions is transfusion of the incorrect ABO group blood. The ABO system is by far the most significant of all the antigen–antibody groups in transfusion practice. The ABO classification is the only blood group system in which patients have antibodies to antigens that have never been present in their system. In other blood group systems there needs to be an exposure to the antigen through prior transfusion or pregnancy.
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Patients are categorized into an ABO blood group (Table 196-1). The system is comprised of four groups (O, A, B, and AB) and four components (two antigens and two antibodies). If the patient has blood group A, they have A antigens on the surface of their red blood cells and B antibodies in their plasma. If the patient has blood group B, they have B antigens on the surface of their red blood cells and A antibodies in their plasma. If the patient has blood group AB, they have both A and B antigens on the surface of their red blood cells and no A or B antibodies in their plasma. If the patient has blood group O, they have neither A nor B antigens on the surface of their red blood cells but they have both A and B antibodies in their plasma. Table 196-2 illustrates the possible combinations of antigens and antibodies with the corresponding ABO type.
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The Rh system classifies blood groups according to the presence or absence of the Rh antigen in the red blood cells. Rh-positive blood given to a Rh-negative patient can be dangerous. Symptoms may not occur the first time Rh-incompatible blood is given. Rh antibodies are IgG antibodies which are acquired through exposure to Rh-positive blood (commonly through pregnancy or transfusion of blood products). If the patient is exposed to Rh-positive blood after the antibodies form, antibodies will attack the foreign red blood cells, causing hemolysis.
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A person with type O blood is said to be a universal donor. A person with type AB blood is said to be a universal recipient. In an emergency, type O Rh-negative blood can be given because it is most likely to be accepted by all blood types.
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