Transfusion medicine

• Red blood cell (RBC) alloimmunization is the formation of antibodies to non-self RBC antigens (excluding naturally occurring anti-A and anti-B)
• Only occurs after exposure through transfusion, pregnancy or transplantation
• Incidence varies among different patient populations and is estimated to occur in 0.5 - 3% of the general population

• Presence of RBC alloantibodies can complicate pretransfusion testing and delay blood product availability
• In non-alloimmunized patients, antigens other than ABO and RhD are not routinely considered in blood product selection for transfusion
• To prevent alloimmunization, RhD negative recipients (especially individuals of childbearing potential) should receive RhD negative red blood cells
• Monoclonal antibody therapies such as daratumumab (anti-CD38) interfere with pretransfusion antibody testing by causing panreactivity in indirect antiglobulin test and masking alloantibodies (AABB: Mitigating the Anti-CD38 Interference with Serologic Testing [Accessed 16 December 2021])

• Assessment: Routine antibody testing demonstrated an unexpected antibody in 1/3 of the cells on the antibody screen and a full antibody panel demonstrated positivity in 4/12 cells with a negative auto control. An anti-E was identified while all other common clinically significant alloantibodies were ruled out. Anti-E is part of the Rh blood group system and can cause hemolytic transfusion reactions and hemolytic disease of the fetus and newborn (HDFN).
• Plan: E negative RBC units will be issued for all future transfusions. Please allow extra time for antihuman globulin (AHG) or Coombs crossmatch testing (1 hour).

Which patient scheduled for surgery is most likely to have a red blood cell antibody?

1. 8 year old child with congenital heart disease
2. 26 year old woman with fibroids
3. 60 year old woman who had a previous spinal surgery and has 2 children
4. 65 year old man with 4 children and coronary artery disease

C. 60 year old woman who had a previous spinal surgery and has 2 children. The patient who has a history of pregnancy and previous surgery with likely transfusion is most likely to have an RBC antibody. RBC alloimmunization occurs after exposure to non-self antigens through pregnancy, transfusion or transplantation.

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Reference: Red blood cell alloimmunization

Patients with which disease have the highest red blood cell alloimmunization rates?

1. Acute leukemia
2. Iron deficiency anemia
3. Sickle cell disease
4. Solid tumor malignancy

C. Sickle cell disease. Patients with sickle cell disease have higher rates of RBC alloimmunization (19 - 43%) compared with 1 - 3% of the general population. Higher rates of RBC alloimmunization are also seen in patients with thalassemia major (5 - 45%) and myeloproliferative syndromes (15 - 59%) as well as patients with warm autoantibody mediated hemolytic anemia.

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Reference: Red blood cell alloimmunization