Adsorption procedure to remove WAA using allogeneic RBCs. Example of the multistep process for allogeneic adsorptions to remove WAA to identify whether an underlying alloantibody is present (eg, anti-Jk^a). Three donor RBCs of known phenotypes (ie, R₁R₁, R2R2, and rr) are selected and treated with enzyme or ZZAP. The patient's serum (or plasma) is added to an aliquot of each of the 3 donor RBCs and incubated for 10 to 60 minutes at 37 °C. Three separate adsorptions are performed, each undergoing 1 to 4 rounds of adsorption in which the patient's serum is repeatedly incubated with a new set of donor RBCs. Following an adequate number of adsorptions, adsorbed serum samples are tested against reagent RBCs. If 1 or more aliquots are positive, an alloantibody can be identified based on the pattern of reactivity and knowledge of the antigens expressed on each aliquot of donor RBCs used for adsorption.