Section III. RED BLOOD CELL ANTIBODIES
a. Alloantibodies are found in people who, through pregnancy, previous
transfusion, or injections, have been exposed to foreign RBC antigens. Some people
with no known immune stimulus may have unexpected antibodies, usually reacting at
b. Unexpected antibodies may be responsible for the following:
(1) A discrepancy between ABO and serum-grouping. This may be caused
by any antibody reacting at room temperature with antigenic determinants, other than
ABO, on the reagent RBCs.
(2) A positive antibody-screening test. Properly selected reagent RBCs
should detect 95 percent or more of clinically significant antibodies.
(3) An incompatible crossmatch. The donor's RBCs contain one or more
antigens, reacting with antibodies, in the serum of the patient.
(4) A transfusion reaction. A new antibody, in a recently transfused person,
an anamnestic response caused by an antibody too weak to demonstrate before
transfusion, or an antibody that was missed in pretransfusion testing may cause a
(5) Jaundice in a newborn. Both the serum of the mother and of the baby,
and their RBCs must be studied. Unusual problems sometimes require study of the
father's cells and those of other family members.
(6) A positive direct antiglobulin test. Antibodies may be identified in the
serum, or in an eluate prepared from the RBCs. In some cases, antibodies may be
directed against a drug, rather than RBC antigens.
(7) A positive autocontrol. Agglutination may be observed after room
temperature (RT) or 37C incubation and indicate the presence of cold or warm
autoantibodies, fatty acid-dependent antibodies, or abnormal proteins causing heavy