The major antigens in the ABO system are A and B. An individual with A antigens has type A blood; an individual with B antigens has type B blood. A person with both A and B antigens has type AB blood, and one having neither A nor B antigens has type O blood. The genes determining the presence or absence of A or B antigens reside on chromosome number 9.² Immunologically competent individuals more than 6 months of age have serum antibodies that react with the A and B antigens absent from their own red cells (Table 4-1). Thus, a person with type A blood has anti-B antibodies, whereas one with type B blood has anti-A antibodies.

Individuals with type AB blood have neither of these antibodies, whereas those with type O blood have both. These antibodies are not inherited, but develop after exposure to environmental antigens that are chemically similar to red cell antigens (e.g., pollens and bacteria). Individuals do not, however, develop antibodies to their own red cell antigens.^3,4

Anti-A and anti-B antibodies are strong agglutinins and cause rapid, complement-mediated destruction (see Chapter 3 - Immunology and Immunologic Testing) of any incompatible cells encountered. Although most of the anti-A and anti-B activity resides in the IgM class of immunoglobulins (see Chapter 3 - Immunology and Immunologic Testing), some activity rests with IgG. Anti-A and anti-B antibodies of the IgG class coat the red cells without immediately affecting their viability and can readily cross the placenta, resulting in hemolytic disease of the newborn. Persons with type O blood frequently have more IgG anti-A and anti-B antibodies than do individuals with type A or B blood. Thus, ABO hemolytic disease of the newborn (erythroblastosis fetalis) affects infants of type O mothers almost exclusively.⁵

When blood transfusions are required, the client is normally given blood of his or her own type to prevent adverse antigen-antibody reactions. In emergency situations, however, some individuals may be given blood of other ABO types. For example, because type O blood has neither A nor B antigens, it may be given to individuals with types A, B, and AB blood. Thus, a person with type O blood is called a universal donor. With the advent of colloid expanders (e.g., dextran), untyped blood is not given even in cases of hemorrhage. Further, because persons with type O blood have both anti-A and anti-B antibodies, they can receive only type O blood.

The situation is reversed for those with type AB blood. Because these individuals lack anti-A and anti-B antibodies, they may receive transfusions of types A, B, and O blood in emergencies when type AB blood is not available. Thus, a person with type AB blood is called a universal recipient.

ABO blood typing is an agglutination test in which the client's red cells are mixed with anti-A and anti-B sera, a process known as forward grouping. The procedure is then reversed, and the person's serum is mixed with known type A and type B cells (i.e., reverse grouping). When a transfusion is to be administered, cross-matching of blood from the donor and the recipient is performed along with typing. Cross-matching detects antibodies in the sera of the donor and the recipient that could lead to a transfusion reaction as a result of red cell destruction.

Other pretransfusion or post-transfusion tests can be performed to determine the cause of transfusion reactions. The leukoagglutinins are antibodies in the donor blood that react with white blood cells in the recipient's blood, producing fever, cough, dyspnea, and other lung complications, depending on the severity of the reaction after the transfusion. Such a reaction requires that leukocyte-poor blood be used to transfuse these clients. Platelet antibody tests are performed to detect specific antibodies that cause post-transfusion purpuric reactions. Assays as well as platelet typing can be performed to support a diagnosis of post-transfusion purpura and thrombocytopenic purpura.⁶

• The normal distribution of the four ABO blood groups in the United States is shown in Table 4-1. Discrepancies in the results of forward and reverse grouping may occur in infants, elderly persons, and persons who are immunosuppressed or who have a variety of immunologic disorders.⁷

• Identification of the client's ABO blood type, especially before surgery or other procedures in which blood loss is a threat or for which replacement may be needed, or both
• Identification of donor ABO blood type for stored blood
• Determination of ABO compatibility of donor's and recipient's blood types
• Identification of maternal and infant ABO blood types to predict potential hemolytic disease of the newborn

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• Immunosuppressive drugs taken by the client or the presence of an immunologic disorder should be noted.

A venipuncture is performed and the sample collected in a red-topped tube or other type of blood collection tube, depending on laboratory preference. The sample must be handled gently to avoid hemolysis and sent promptly to the laboratory.

Although correct client identification is important for all laboratory and diagnostic procedures, it is crucial when blood is collected for ABO typing. One of the most common sources of error in ABO typing is incorrect identification of the client and the specimens.⁸

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• The client should be informed of his or her blood type, and the information should be recorded on a card or other document (e.g., driver's license) that the client normally carries in the event of an emergency requiring a blood transfusion.
• Circulatory overload: Report increased blood pressure; bounding pulse; and signs of pulmonary edema such as dyspnea, rapid and labored breathing, cough producing blood-stained sputum, and cyanosis.
• Blood transfusion reaction: Note and report reduced blood pressure, elevated temperature, chills, palpitations, substernal or flank pain, warmth at the infusion site, or anxiety. Discontinue transfusion and infuse saline. Send the leftover unit of blood and a blood and urine specimen to the laboratory.
• Critical values: Notify physician immediately if an incompatible cross-match occurs.