In order to determine the antibody causing the reactions, you must perform rule-ins and rule-outs on your panel(s).
To perform rule-outs, look at the cells causing negative reactivity. The antigens present on that reagent cell line, indicated by a +, can be ruled out from causing the reactions because they are on a cell that displayed a negative reaction. To be ruled out, the antigen needs to be homozygous positive on that cell. Heterozygous cells have fewer antigens and can cause weaker reactions. There are a few antigens that can be ruled out on 2 heterozygous cells: C, E, and K. Once ruled out, that antigen can be crossed out at the top of the panel.
To perform rule-ins, look at the cells causing positive reactivity. The antigens present on that reagent cell line, indicated by a +, can be looked at as a possible cause for the reactions while keeping in mind the antigens that have already been ruled out. Looking for patterns in the panel reactions can help you to determine your next steps to rule in that antibody, determine if there are multiple antibodies, and rule out additional antibodies. To rule in an antibody, you need 3 positive reagent cells with that antigen present. These cells can be homozygous or heterozygous for the antigen.
You may need to run additional panel cells to rule in or rule out different antibodies. Select cells that are positive for the cells that you are trying to rule in while also negative for cells that you are trying to rule out. To select rule out cells, select cells that are homozygous positive for the antibodies that you are ruling out, but negative for the antibodies that you suspect are causing the patient's reactions.
If your Autocontrol on your panel is positive, the panel is invalid. You cannot determine from that panel if the reactions are due to an alloantibody or an autoantibody. Further tests will need to be run to determine the cause of the positive antibody before running further panel cells.
Antibody detection, to include rule-ins and rule-outs, may be different at each institution. Follow your institution's policies and procedures.
In the cases that follow, you may not be able to completely rule in or rule out all antibodies, but you will be able to select the most likely culprit. For a more thorough look at the process of antibody screening and identification, please refer to our course titled Antibody Detection and Identification.
