Probability plays a crucial role in transfusion medicine, with medical decisions being informed by statistical metrics derived from valuable scientific data. The process of ruling out involves a statistically based measure that employs a 95% confidence level to confirm the presence of a suspected antibody. The idea is that if the detective can rule out enough suspects, they can assert with a high degree of certainty that the identified antibody is indeed the culprit.
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 antibody/antigen reaction. In other words, the absence of a reaction is noted with a cell that is positive for the corresponding antigen.
Rule-out is not an infallible method and comes with its limitations. It's possible that it may not always be effective. 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 (negative) cells are selected for rule-out. To be classified as non-reactive, a cell should not have reacted in any phase of testing in a given panel or screen. 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.
In the case of cold antibodies, if reactions only occur 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).
