Molecular DNA ‐based testing for blood group antigens: recipient–donor focus

DNA‐based testing for blood group antigens has become commonplace in a number of clinical situations to improve transfusion therapy for blood transfusion recipients. These include typing for antigens in patients who are multiply transfused to determine which blood group antibodies may be present, typing when the red blood cells (RBCs) are coated with immunoglobulin, and typing for uncommon antigens, especially when no serologic reagent is available. Other clinical applications include resolving ABO typing discrepancies for patients awaiting transplant, or determination of the original type of a bone marrow transplant recipient, or confirmation of an ABO subgroup in a kidney donor. Testing for the specific mutation associated with depressed Kell system antigens in McLeod syndrome may also have value because different mutations appear to be associated with prognosis. Applications in prenatal medicine include discrimination between weak D and partial D to determine if a pregnant woman is a candidate for Rh immune prophylaxis, and assessing the risk for hemolytic disease of the fetus or newborn and neonatal thrombocytopenia. Assessing risk includes testing the paternal sample for the target antigen, and if positive testing for gene copy number (zygosity) and testing the fetus from amniocentesis or non‐invasive maternal plasma sample. Donor centers are now able to screen large numbers of donors to label antigen‐negative RBC products. DNA typing will change transfusion practice by allowing patients facing chronic transfusion therapy to have a more comprehensive blood group antigen profile performed, and to receive donor units antigen‐matched for more than ABO and RhD to reduce alloimmunization. A patient who makes an alloantibody to a RBC antigen is forever at risk for his or her lifetime; for a serious transfusion reaction if ever requiring transfusion in an emergency, and also for a high risk pregnancy if a woman of child bearing age. Prevention of alloimmunization is an important advance in transfusion safety and is now possible with electronic patient medical records and testing and labeling of blood products for additional blood group antigens.