SPECIFICITY OF AUTOANTIBODY
a. Warm Autoimmune Hemolytic Amenia. The specificity of autoantibodies
associated with warm autoimmune hemolytic amenia (WAIHA) is very complex.
Specificity is often directed against the Rh antigen complex, but this can only be
determined if RBCs of very rare phenotypes are available, such as -D-or Rh null. Apart
from Rh specificity, there have been reports of warm autoantibodies with anti-A, Ena, -
Ge, -lt, -JKa, -K1, -K4, -K5,-K13. -Lan, -LW, -Nn, -Sci, -U, -Wrb, and Xga specificities. It
is seldom necessary to perform additional testing to determine the autoantibody
specificity and then to select antigen-negative blood for transfusion. In some patients,
simple specificity will be readily apparent (for example, autoanti-e). When there is
evidence of immune hemolysis and the simple autoantibody specificity is clear-cut-not-
relative, there may be some benefit in providing antigen negative blood. However, it is
important not to expose patients to Rh antigens that their own cells lack, especially D.
In instances where apparent specificity is directed to a high-incidence antigen or when
the autoantibody fails to react with red cells of an uncommon Rh phenotype (for
example, -D- Rh null), the compatible donor blood is unlikely to be available for
transfusion. Thus, there is no point to determine specificity in the first place. If such
blood is available, it should be reserved for alloimmunization (antibodies are developed
in response to antigens from genetically dissimilar individuals of the same species)
patients of that uncommon phenotype.
b. Specificity of Cold Aggutinins. If the patient has cold autoaggautinins, the
specificity is usually within the Ii system. In addition to testing the serum against a cell
panel, the serum is titrated against adult I cells, cord i cells, and, if possible, adult i cells
at various temperatures (for example, 4C, 30C, or 37C). In this way, a cold agglutinin
titer specificity and thermal range are determined using one set of master dilutions.
COLD AGGLUTININ TITER. THERMAL AMPLITUDE, AND CONFIRMATION
OF ANTI-l(i) SPECIFICITY
a. Procedural notes are to be followed.
(1) A master series of doubling dilutions of serum is made in isotonic saline
from 1:1 to 1:8,000 (approximately 0.2-ml aliquots).
It is extremely important to use separate pipettes for each tube when
preparing the dilutions to prevent "carry over." If a single pipette is used
throughout, falsely high results occur (for example, a titer of 1:100,000 may
be 1:4,000 when separate pipettes are used).
(2) Starting from the highest dilution, two drops are transferred to three
10- X 75-mm tubes.
(3) The tubes are placed in a 37C water bath and allowed to reach 37C
(for example, 10 minutes).