Principle Elution refers to any number of methods available to cause dissociation of bound antibody molecules from red cells. Each method alters some aspect of the physical environment of the coated red cells, so that conditions become unfavourable for antigen-antibody complexes to remain together. The fluid obtained for testing is called an eluate. If properly prepared and controlled, the eluate can be tested in the same manner as serum for the presence of antibody activity. Procedure Red cells must be very thoroughly washed prior to the performance of any elution procedure.
Washing removes unbound antibody from around the cells.
If washing is incomplete, free antibody may appear in the eluate and be wrongly assumed to have been recovered from the red cells. Complete resuspension prior to adding saline to the cell pack and sufficient centrifugation to drive all of the cells to the bottom of the tube during each wash ensures maximal efficiency of the washing procedure. Washing efficiency should be monitored by testing the supernatant saline, sampled from directly over the cell pack after the final wash in parallel with the eluate. No free antibody should be present in this last wash solution. If the final wash gives a positive result, reactivity in the eluate cannot be assumed to represent recovery of antibody from the red cells.