Before RBC transfusions as part of a "type and screen" or "type and crossmatch"
In the investigation of a suspected transfusion reaction
To help determine if hemolytic anemia may be caused by an autoantibody directed against a person's own red cells
If clinically significant RBC antibodies have been identified during pregnancy, the baby's condition will be monitored. Whether or not the antibodies will affect the baby's condition depends upon the antibody present and the RBC antigens that the fetus has inherited. Some antibodies can cross the placenta from mother to baby and cause HDN.
The RBC antibody identification test is used to name the specific antibody or antibodies that are present to determine if they are likely to be clinically significant, i.e., if they are likely to cause a transfusion reaction. Some RBC antibodies are known to cause moderate to severe reactions while other less significant ones may cause a positive test but few to no symptoms or complications in the blood transfusion recipient or baby.
For blood transfusions, if one or more clinically significant RBC antibodies are identified, then donor blood that lacks the corresponding RBC antigens must be used for transfusion. When someone has a condition that requires recurrent transfusions, they are exposed to many foreign RBC antigens and may develop multiple RBC antibodies over time, making the process of finding compatible blood increasingly challenging.
Sometimes an RBC antibody may be present in such a small quantity that it does not cause a positive RBC antibody screen during pre-transfusion blood compatibility testing. Once a person has developed an RBC antibody, he must always be matched with antigen-negative blood, even if the antibody is no longer detectable since after the blood is given to the recipient, it can trigger renewed, rapid antibody production and cause a delayed hemolytic transfusion reaction several days later.
The antibody identification test may be ordered when an RBC antibody screen or a DAT is positive. The test may also be performed when a person has a transfusion reaction or when a mother has a baby with HDN.
Results of RBC antibody identification will name the specific antibody or antibodies present in the blood of the person tested. If the antibody identified is considered clinically significant, then it will need to be taken into account with each transfusion and/or pregnancy. If an antibody is not considered clinically significant, then it is not likely to cause a transfusion reaction in the person or cause hemolytic disease of the newborn. For blood transfusions, it is not necessary to find compatible blood if the antibody identified is not likely to cause a transfusion reaction (is not clinically significant).
Examples of RBC antibodies and their clinical significance are shown in the table below.
Some RBC antibodies are naturally-occurring; they do not require an initial exposure to the specific targeted antigen. These include antibodies that correspond to the major A and B red blood cell antigens.
RBC antibodies are not the only things that can cause a transfusion reaction. The recipient's immune system may also react to someone else's white blood cells or platelets, or to drugs that the donor may have taken. Rarely, antibodies in the plasma of the blood donor may target the RBCs of the transfusion recipient if products with a large amount of plasma are transfused.
An RBC antibody can occasionally be missed with antibody identification testing if the antibody is low titer or formed against a rare antigen. This is why the crossmatching process is important even in patients with no demonstrated antibodies. It evaluates the compatibility of the donor's red blood cells and recipient's serum for each unit of RBCs transfused (see Blood Banking).
This article was last reviewed on March 22, 2013. | This article was last modified on June 4, 2014.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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