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The page below is a sample from the LabCE course Antibody Detection and Identification. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Rule-Out Procedures

Rule-out (also referred to as exclusion or cross-out) is a process by which antibodies are identified as being unlikely in a given sample due to the absence of an expected antigen-antibody reaction. In other words, the absence of a reaction is noted with a cell that is positive for the corresponding antigen. Antibodies that could not be responsible for the reactions seen are excluded or ruled-out.

Rule-out, while very useful, can lead to error. Ruling out an antibody should be combined with other supporting data to increase confidence in the solution; the more data collected, the higher the probability that the final solution is correct.

Non-reactive cells are selected for rule-out. To be classified as non-reactive, a cell must NOT have reacted in any phase of testing in a given panel or screen.

In the case of cold antibodies: if reactions are only occurring at immediate spin and are negative in the AHG phase, then that panel cell can be used as a rule out cell for IgG reactive antibodies but not for antibodies that react at immediate spin (IgM).

If there is no reaction with a panel cell then it is possible that antibodies to the antigens on that panel cell are not present in the sample being tested.