Which antigens show dosage

Using the logic that if the rule-out cell is positive for a given antigen, it should have reacted with the corresponding antibody, the technologist can rule-out antibodies that correspond to antigen-positive cells.

For example, cell 3 in the screen above is positive for big K. If anti-K were present, it should have reacted. It did not react. Therefore, anti-K is most likely NOT present and can be presumptively ruled-out. To increase the probability that rule-out will not mistakenly eliminate a weakly-reacting antibody that exhibits dosage, most laboratories will rule-out using only cells that are homozygous for the corresponding antigen for those systems that generally show dosage.

For example, in the screen above, cell 3 is homozygous positive for c c positive, C negative. As shown in Table , anti-c reacts more strongly with homozygous cc cells than it does with heterozygous Cc cells, as does anti-e. Note that if the antibody is weak, it may give a false negative result with heterozygous cells. This is why it is important that antibody screen cells be homozygous for antigens that show dosage.

In the Rh system, C, c, E and e antigens show dosage. The D antigen does not show dosage in the usual sense, because the d antigen does not exist. However, the amount of D antigen does vary significantly from person to person according to the person's Rh genotype.