Once an antibody hypothesis is generated, additional reagent red blood cells may be selected and tested against patient serum/plasma to rule out any other commonly encountered antibodies that could not be ruled out with the initial antibody screen and panel. Cells should be selected that are negative for the antigen(s) that correspond to the suspected antibody and positive for the antigen(s) to commonly encountered antibodies that have not been ruled out. If not ruled out, laboratories often select cells for at least the following: anti-D, anti-C, anti-c, anti-E, anti-e, anti-K, anti-k, anti-Fya, anti-Fyb, Anti-Jka, anti-Jkb, anti-Lea, anti-Leb, anti-P1, anti-M, anti-N, anti-S, and anti-s.
Antibodies to antigens of very low incidence (for example, anti-Jsa) are generally not eliminated in initial testing, but in most settings, it is not feasible to try and find rule-out cells. In these cases, it is important for the blood bank scientist to understand that these antibodies have not been ruled out due to limitations in the test system.