After the ABO system, the Rh system is the group of red cell antigens with the greatest importance.⁹ The antigen was called the Rh factor because it was produced by immunizing guinea pigs and rabbits with red cells of rhesus monkeys. Researchers found that the serum from the immunized animals agglutinated not only the rhesus monkey red cells but also the red cells of approximately 85 percent of humans. Thus, human red cells could be classified into two new blood types: Rh-positive and Rh-negative. This discovery was a great breakthrough in explaining transfusion reactions to blood that had been tested for ABO compatibility as well as in explaining hemolytic disease of the newborn not caused by ABO incompatibility between mother and fetus.¹⁰

We now know that the Rh system includes many different antigens. The major antigen is termed Rh_o or D. Persons whose red cells possess D are called Rh-positive; those who lack D are called Rh-negative, no matter what other Rh antigens are present, because the D antigen is more likely to provoke an antibody response than any other red cell antigen, including those of the ABO system. The other major antigens of the Rh system are C, E, c, and e.¹¹ Among blacks, there are many quantitative and qualitative variants of the Rh antigens that do not always fit into the generally accepted classifications.¹²

Rh-negative individuals may produce anti-D antibodies if exposed to Rh-positive cells through either blood transfusions or pregnancy. Although 50 to 70 percent of Rh-negative individuals develop antibodies if transfused with Rh-positive blood, only 20 percent of Rh-negative mothers develop anti-D antibodies after carrying an Rh-positive fetus. This difference occurs because a greater number of cells are involved in a blood transfusion than are involved in pregnancy.

When Rh antibodies develop, they are predominantly IgG. Thus, they coat the red cells and set them up for destruction in the reticuloendothelial system. The antibodies seldom activate the complement system (see Chapter 3 - Immunology and Immunologic Testing). Anti-D antibodies readily cross the placenta from mother to fetus and are the most common cause of severe hemolytic disease of the newborn. Immunosuppressive therapy (e.g., with Rh_o[D] immune globulin [RhoGAM]) successfully prevents antibody formation when given to an unimmunized Rh-negative mother just after delivery or abortion of an Rh-positive fetus.¹³

Rh typing involves an agglutination test in which the client's red cells are mixed with serum containing anti-D antibodies. Agglutination indicates that the D antigen is present, and the person is termed Rh-positive.

• The D antigen is present on the red cells of 85 percent of whites and a higher percentage of blacks, Native-Americans, and Asians.

• Identification of the client's Rh type, especially before surgery or other procedures in which blood loss is a threat or for which replacement may be needed, or for both
• Identification of donor Rh type for stored blood
• Determination of Rh compatibility of donor's and recipient's blood
• Identification of maternal and infant Rh types to predict potential hemolytic disease of the newborn
• Determination of anti-D antibody titer after sensitization by pregnancy with an Rh-positive fetus
• Determination of the need for immunosuppressive therapy (e.g., with RhoGAM) when an Rh-negative woman has delivered or aborted an Rh-positive fetus

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).

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.

As with ABO typing, correct client and sample identifications are crucial in avoiding erroneous results.

Nursing Care After the Procedure

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

• As with ABO typing, the client should be informed of his or her Rh type.
• Women of childbearing age who are Rh-negative should be informed of the need for follow-up should pregnancy occur.
  • Rh incompatibility: Note and report Rh factors of mother and father, number of pregnancies, and past transfusions of Rh-positive blood given to an Rh-negative mother. Communicate incompatible test results to the physician. Inform client and prepare client for administration of Rh immunoglobulins (RhoGAM).