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Antibody Adsorption Procedures

Sometimes, patients with autoantiobodies require red cell transfusion. The most important technical issue faced by the transfusion service is determining if the patient’s serum contains alloantibodies in addition to the autoantibody. Between 15 and 40% of patients with autoimmune hemolytic anemia have alloantibodies. The most common alloantibodies detected in the sera of patients with AIHA in descending order are: anti-E, K, C, Fya, Jka, and c.

The most frequently used method for detecting alloantibodies in the presence of a broadly reactive autoantibody is the warm autoadsorption procedure. Autoantibody is removed from autologous red cells by heat or chemical treatment and then the red cells are treated with an enzyme to enhance autoantibody adsorption. The most popular technique is to treat red cells with ZZAP, which is a combinination of dithiothreitol and papain. Autoantibody is then adsobed from plasma with these treated autologous red cells. Several adsorptions may be necessary to remove all of the autoantibody. If no antibody is detected, the adsorbed plasma can be used for crossmatching donor units. If alloantibody is present, it must be identified and antigen negative units selected for crossmatching.

The warm autoadsorption procedure is not useful in patients who have been transfused within the past 30 days because even a small percentage of transfused cells may adsorb alloantibody, producing a falsely negative result. In this situation, allogeneic adsorptions may be required. By selecting two or three samples of red cells of varying phenotypes, almost all clinically significant alloantibodies can be detected. For example, adsorbing a serum containing an autoantibody and an anti-Jka alloantibody with Jka negative red cells will remove the autoantibody but not the anti-Jka . Once the autoantibody is removed, the remaining alloantibodies can be identified using a panel. This procedure is usually performed at a blood center reference laboratory instead of a hospital transfusion service.

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