Routine Workflow for Serologic Testing in the Transfusion Service. Once the patient’s red blood cells (RBCs) are phenotyped for ABO and RhD antigens, providing appropriate ABO- and RhD-matched RBCs for transfusion is straightforward if no alloantibodies or autoantibodies are detected. However, if the patient’s serum or plasma reacts with reagent RBCs, the specificity of each antibody present must be identified. The patient’s own RBCs are phenotyped to confirm the validity of antibody identification. In the presence of autoantibody or an antibody that reacts with a very high frequency antigen, the process of antibody identification and phenotyping of the patient’s RBCs becomes technically difficult, often requires the availability of rare reagent cells and sera, and is highly time-consuming.