d. Weak antibodies may be reacting only with RBCs from donors homozygous
for the antigen concerned or only with those cells possessing the strongest antigens.
e. The antibody may be reacting with an antigen for which the RBCs have not
been tested. For example, the antibody may be reacting with 65 percent of random
donors and with several cells of the panel, but without a specific pattern. If the pattern
has not been typed for Dombrock (Doa), one might suspect this antibody.
f. The antibody may be directed against a low-frequency antigen not present on
the panel. This is usually encountered when the cross match or antibody-screening test
is positive, and the panel is negative. The antigen is on the screening cells of the
donor's cells, but not on any other cells tested. The commercial distributors of the cells
frequently have Information about the cells that are not on the protocols distributed.
They will provide this information on request. Antibodies to low -incidence antigens may
cause hemolytic disease of the newborn, in which case, maternal antibody reacts only
with the RBCs of the infant, the father, and possibly some members of his family, but
the antibody-screening test and panel results are negative. These cases can
sometimes be identified by testing the father's cells with known antibodies for low-
incidence antigens and testing the unknown antibody against cells known to possess
g. When all cells are agglutinated, the antibody may be reacting with a high-
incidence antigen. Test the antibody with known cells that lack high-incidence antigens,
and test the patient's pretransfusion cells with known antibodies for high-incidence
antigens. If a patient lacks a high-incidence antigen and has an antibody that reacts
with all the cells tested, chances are very good that the antibody is directed against that
antigen. It is wise to use several cells that are negative for their high-incidence antigen
in order to demonstrate the presence of any other antibodies. Persons, who have
developed one antibody, and have proved their antibody production ability should be
suspected of having more than one antibody until proved otherwise. Compatible donors
suspected can sometimes be found among the siblings of the patient, and usually from
the AABB Rare Donor File.
h. When all the panel cells react by forming weak, fragile agglutinates, the
antibody may have one of the high-titer, low-acidity specificities. These are a group of
antibodies that may show titers into the hundreds; but not more than two plus reactIons
in the strongest dilution. Two of these, anti-Chido (Cha) and anti-Rodgers (Rga), can be
inhibited by plasma from Ch (a+) and Rg (a+) persons, but not by other secretions.
Many of these antibodies have been shown to be related to antigens on white cells.
Some distinguishing features are shown in Table 1-7.