Red Cell Alloimmunization

Description

When antibodies are formed against foreign antigens from one's own species, the process is termed alloimmunization and the antibodies are called alloantibodies (as opposed to forming autoantibodies to one's own antigens or forming xenoantibodies to antigens from a foreign species).

RBC alloimmunization is the formation of antibody/antibodies by the recipient to red blood cell antigens from previous transfusion or pregnancy. Occasionally RBC alloimmuniaztion occurs without prior exposure to foreign RBC antigens; in this case presumably the stimulus is from antigens located outside the RBC membrane, or from other substances such as bacteria. Examples of this are Chido/Rogers, present on the complement component C4, or Bgª/Bgb which are leukocyte antigens whose corresponding antibodies may also react with red cells. Ingestion or inhalation of certain bacteria, or substances in the environment which are antigenically similar to RBC alloantigens may result in the formation of “naturally occurring” (usually IgM) antibodies.

Incidence

The incidence of alloantibodies varies widely according to patient disease, prior history of transfusion, pregnancy and the antigen frequencies of patients versus donors in a geographic location.

The incidence of red cell antibodies is estimated to be 1-2 per cent in the general hospital population, 5 per cent or more in multi-transfused patients and multiparous females, and 20 per cent or more in patients with transfusion-dependent diseases (e.g., sickle cell anemia, thalassemia, etc).