Identification of Alloantibody After Homologous Adsorption
Anti-S would remain in the serum after homologous adsorption using R2R2, ss, Fy(a-b+), Jk(a+b-), kk red blood cells.
Analysis of the Adsorption Process
When performing homologous adsorption using phenotypically matched RBCs, any alloantibodies directed against antigens present on the adsorbing cells will be removed from the serum. To determine which alloantibody would remain, we must analyze which antigens are present on the adsorbing cells:
- R2R2 phenotype: This indicates DCcEe (presence of D, C, E antigens)
- ss: Indicates absence of S antigen
- Fy(a-b+): Indicates presence of Fyb antigen, absence of Fya
- Jk(a+b-): Indicates presence of Jka antigen, absence of Jkb
- kk: Indicates absence of K antigen
Reasoning for Anti-S Remaining
Since the adsorbing RBCs are phenotyped as "ss" (S-negative), any anti-S antibody in the patient's serum would not be adsorbed by these cells. Therefore, anti-S would remain in the serum after the adsorption procedure.
The other potential alloantibodies would be adsorbed:
- Anti-E would be adsorbed because the R2R2 phenotype includes E antigen
- Anti-Jka would be adsorbed because the cells are Jk(a+)
- Anti-Fyb would be adsorbed because the cells are Fy(b+)
Clinical Significance
This scenario is particularly important given the patient's recent transfusion history (2 months ago). The American Society of Hematology guidelines emphasize the importance of extended antigen matching, including S/s antigens, to prevent alloimmunization in patients requiring multiple transfusions 1.
When working with patients who have warm autoantibodies, adsorption techniques are essential to detect underlying alloantibodies that may cause hemolytic transfusion reactions. Even small amounts of antigen-positive RBCs (as little as 2-6%) can completely remove alloantibodies during adsorption procedures 2, which is why using phenotypically matched RBCs that lack specific antigens is crucial for detecting clinically significant alloantibodies.
Transfusion Considerations
For patients with warm autoantibodies requiring transfusion, identifying underlying alloantibodies is critical for preventing hemolytic transfusion reactions. The ASH guidelines recommend extended red cell antigen matching (including Jka/Jkb, Fya/Fyb, S/s) to provide further protection from alloimmunization 1.
In this case, since the patient has a warm reacting autoantibody and needs packed cells, identifying the anti-S alloantibody is essential for selecting appropriate units that are S-negative to prevent a potential hemolytic transfusion reaction.