Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1158 page)

   The forward and reverse ABO blood grouping of all patients must be determined prior to the transfusion of blood products using commercial reagents and the patient’s red cells and serum (or plasma).

   The forward ABO blood grouping is determined by checking the patient’s (or donor’s) red cells for the presence of A and B antigens using commercial anti-A and anti-B reagent antibodies.

   The reverse ABO grouping is determined by checking the patient’s (or donor’s) serum for the presence of anti-A and anti-B antibodies using commercial reagent red cells.

   The strength of the agglutination during testing is usually graded.

   A group A individual has anti-B but not anti-A antibodies. A group B individual has anti-A but not anti-B antibodies. A group AB individual has neither anti-A nor anti-B antibodies. The serum of group O persons contains both anti-A and anti-B antibodies.

   Rh Typing

   The Rh (D) type of all patients should be determined prior to transfusion or if the patient is pregnant in order to prevent immunization to the D antigen and production of the anti-D alloantibody. Anti-D is a clinically significant antibody that can cause hemolytic transfusion reactions and hemolytic disease of the fetus and newborn (HDFN).

   The Rh typing is performed by testing the RBCs for the presence of D antigen using anti-D reagent antibodies and checking for agglutination.

   Some patients may not show clear agglutination after centrifugation with anti-D but still have the D antigen. This is known as weak D and requires the addition of AHG for identification of the D antigen. These weak D patients are still considered Rh positive.

   Weak D testing is not required for patients but is required for donors.

   In practice, the terms Rh positive and Rh negative, respectively, refer to the presence or absence of the D antigen and routine pretransfusion tests only include testing for the D antigen. However, in addition to the D antigen, there are many other antigens in the Rh blood group system. When alloantibodies are present, it may be necessary to type patients and/or donors for these (other) Rh antigens, most commonly C, E, c, e.

   Antibodies to Rh antigens are immune stimulated in most cases, mostly following pregnancy or transfusion.