Alloimmune hemolytic anemia occurs when the immune system produces an antibody against foreign or non-self antigens. Examples include:
- Hemolytic transfusion reactions
- Hemolytic disease of the fetus and newborn (HDFN)
Hemolytic transfusion reactions occur immediately or within days of a red blood cell transfusion. The transfusion recipient is exposed to a foreign red cell antigen on the donor cells, which stimulates an immune response. The transfused red cells are sensitized in vivo causing a positive direct antiglobulin test (DAT). Antibodies involved are usually of the IgG classification.
In HDFN, the mother is sensitized to a foreign antigen on the fetal red cells. Sensitization usually occurs through a feto-maternal hemorrhage. The mother will produce an antibody to the foreign red cell antigen. If the antibody is an IgG antibody, it may cross the placenta and bind to fetal cells, causing red cell destruction.
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