Red cell immunology and compatibility testing

Introduction Immunohematology is the study of the immune response to blood cells. This chapter reviews the basic concepts of immunity as they apply to production of antibodies to red blood cells (RBCs), also called atypical alloantibodies. Antibodies to platelets and neutrophils, as well as autoantibodies and drug-induced antibodies, are discussed elsewhere. The relevance of immunohematology to transfusion medicine is addressed through discussion of the principles of serologic and DNA-based testing and the application to blood transfusion and donor–recipient compatibility. Identification of the blood group specificity of alloantibodies (antibody identification) is performed by testing plasma or serum against red cells of known phenotypes. Importantly, modern immunohematology uses knowledge of the blood group antigen profile of the patient to aid and inform the process of antibody identification and selection of units for transfusion. This is feasible with the use of DNA-based testing, which provides an extended RBC antigen profile performed as a single assay. The chapter also includes a discussion of the steps and requirements for pretransfusion compatibility testing and release of blood components for transfusion, as well as efforts to track adverse transfusion events through biovigilance programs and to reduce alloimmunization by extended antigen matching.