The allogeneic adsorption is similar in principle and procedure to the autologous adsorption. However, allogeneic cell aliquots are used in the adsorption process.This method is required when the patient has been recently transfused.
- Ideally, the allogeneic cells that are selected should match the patient's phenotype. Usually two to three different allogeneic cell sets are required. The different allogeneic cells typically have different phenotypes. Usually donors with R1R1, R2R2, and rr phenotypes are chosen. Other antigens to consider when selecting allogeneic cells are K, Fy, Jk, and S. An example would be: The first allogeneic cell may have a phenotype of R1R1, K+, Jk(a-,b+) and the second cell may have a phenotype of R2R2, K-, Jk(a+,b-). (This is only an example, as there are more phenotypes possible). Both cells would have the ability to adsorb the autoantibody from the serum. If there was an anti-Jka present in the serum, for example, it would not be adsorbed by the first cell, but could be adsorbed by the second cell (as the second allogeneic adsorbing cell is Jka antigen positive).
- After the adsorption is complete, the harvested serum/plasma can be used in identification procedures. The serum/plasma obtained from the different allogeneic adsorptions must be analyzed separately against an appropriate panel of cells to achieve identification or exclusion. This is necessary because the difference in phenotypes of the adsorbing cells means the adsorbed serums potentially contain different alloantibodies.
Sometimes, multiple adsorptions are required, depending on the strength of the autoantibody.