Once rule-out is complete, there should be one or more antigens that are not crossed out. The antigen should be present on cells that reacted with the patient's serum and absent on cells that did not react. In this example, the pattern matches perfectly with K. This pattern strongly supports that the patient has anti-K. If other antibodies could not be ruled out, a selected cell panel would need to be performed. (Selecting additional cells is discussed later in this course.)
Note: In cases of multiple antibodies, a perfect matching pattern will be difficult to obtain.
Conclusive antibody identification is attained when the patient's serum is reactive with at least 3 antigen-positive cells and non-reactive with 3 antigen-negative cells. Another confirmation of an alloimmune antibody is the patient's red cell phenotype is negative for the corresponding antigen because alloimmune antibodies can only be produced against antigens the patient's own red cells lack. In the picture below, the positive reactions are circled in yellow and the negative reactions are circled in orange. This patient's red cells should also be K negative (Note: Patient cell phenotyping may not be accurate if the patient has been recently transfused, as any donor cells that are still circulating may be antigen positive, giving a mixed field reaction.)
