(3) The patient's serum is tested against A1, B, O, and his own cells, as
usual. If the patient is known to have, or appears to have, the cold-agglutinin syndrome,
the serum-typing tests should be repeated strictly at 37C. At this temperature, ABO
agglutinins will usually react well, but the cold autoantibody will not react. These results
should be confirmed by the normal methods after the cold autoantibody has been
autoabsorbed from the patient's serum (Lesson 1, Section III).
b. Rh. It is useful to Rh-phenotype patients with AIHA. If the cells have been
separated and washed at 37C, the main problem is that the cells are possibly strongly
sensitized (perhaps with Rh autoantibodies) and will agglutinate spontaneously with the
addition of albumin alone; therefore, when using Rh-typing serums, it is wise to use
antiserums for saline tube test. Unfortunately, many commercial companies add a
small amount of albumin (normally 5 to10 percent) and/or other potentiating media to
such serums and, therefore, patient's cells should always be added to albumin (for
example, 10 percent) as a negative control. An ideal negative control is the actual
diluent that the manufacturer has used to dilute the antiserums, but this is not readily
available for saline tube test reagents. If the albumin antiserums have to be used (for
example, slide and rapid tube reagents), it is important that the diluent supplied by the
same manufacturer of the antiserum be used as a negative control. If this is not
available, then 20 to 30 percent albumin should be used as a control.
AUTOIMMUNE HEMOLYTIC ANEMIA ASSOCIATED WITH WARM
a. Background. This is the most common type of autoimmune hemolytic
anemia (AIHAI). It comprises approximately 66 percent of all cases. There are typical
serologic findings in warm antibody AIHA as noted below.
b. Direct Antiglobulln Test. If anti-lgG and anticomplement monospecific
antiglobulin serums are used, three patterns are found, the most common being RBCs
sensitized with both IgG and complement (about 50 percent of the patients); then;
approximately, 30 percent are sensitized with IgG alone and 20 percent with
complement alone. Sometimes lgA, and/or lgM can also be demonstrated on the RBCs
and rare cases have been described where only lgA or lgM is present.
c. Eluate From Patient's Red Blood Cells. The autoantibody is usually lgG
and can be eluted easily by simple methods, such as heating to 56C or treatment with
ether. It is essential to prepare an eluate in the investigation of AIHA in order to define
the characteristics of the autoantibody. It should be remembered that if the positive
direct antiglobulin test is a result of complement sensitization only, the eluate will
probably have no activity.