When the direct antiglobulin test (DAT) is positive, what is recommended before attempting phenotyping?

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A positive DAT means antibodies are already bound to the patient’s red cells, which can mask the true antigen status of those cells and make serologic phenotyping unreliable. Eluting the bound antibodies pulls them off the red cells, allowing you to test the eluate and identify the antibody’s specificity. Knowing the exact antibody helps distinguish whether you’re dealing with an alloantibody or an autoantibody and clarifies which antigens the patient lacks or expresses, guiding safe transfusion and accurate phenotyping thereafter. Jumping straight to phenotyping can yield misleading results because the coating of the cells by the bound antibody may obscure real antigen expression. The eluate test directly reveals the antibody’s specificity, which is why it’s recommended before phenotyping.