Red Blood Cell Antibody Identification

Antibody identification is used as a follow-up test to a positive indirect antiglobulin test (IAT). The IAT is typically performed during each pregnancy to determine whether the mother has developed any red blood cell (RBC) antibodies and before RBC transfusions as part of a "type and screen" or "type and crossmatch." The antibody identification test is used to determine the RBC antigen(s) that the antibody or antibodies are directed against to determine if they are likely to be clinically significant, i.e., if they are likely to cause a transfusion reaction or hemolytic disease of the newborn (HDN). Some RBC antibodies are known to cause moderate to severe reactions while other less significant ones may cause a positive IAT but few to no symptoms or complications in the blood transfusion recipient or baby.

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.

An IAT and antibody identification test may be used as part of an investigation if a person has a transfusion reaction. Sometimes an RBC antibody may be present in such a small quantity that it does not cause a positive IAT during pre-transfusion blood compatibility testing. But 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.

If RBC antibodies have been identified in a pregnant woman, then the baby's condition will be monitored. Whether or not the antibodies will affect the baby's condition depends upon the antibody present, the RBC antigens that the fetus has, and when the mother's antibodies come into contact with the fetus's blood. Some antibodies can cross the placenta from mother to baby and cause HDN.

The antibody identification test may be ordered whenever an IAT or a DAT is positive and may be repeated when a person has a transfusion reaction or when a mother has a baby with HDN.

When a RBC antibody is identified, it means that an antibody that specifically targets an RBC antigen or antigen group is present in the blood. If the antibody is considered clinically significant, then it will need to be taken into account with each transfusion and/or pregnancy. If it is not considered clinically significant, then it is not likely to cause a transfusion reaction in the patient or hemolytic disease of the newborn.

Examples of RBC antibodies and their clinical significance are shown in the table below.

 

Clinically Significant	Sometimes Clinically Significant	Usually not Significant	Not Considered Significant
Rh (C, E, c, e)	MNS (U, Vw, Mur)	Lutheran (Lua, Lub)	Chido/Rodgers (Cha, Rga)
Kell (K, k, Ku)	Vel	Lewis (Lea, Leb)	JMH
Duffy (Fya, Fyb, Fy3)	Ge	MNS (M, N)	Bg
Kidd (Jka, Jkb, Jk3)	Hy	A1	Csa
Diego (Dia, Dib, Wra)	Yta	P1	Xga
MNS (S, s)

 

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, platelets, and may sometimes form autoantibodies that target their own red blood cells. Rarely, antibodies in the plasma of the blood donor may target the RBCs of the transfusion recipient.

Some RBC antibodies may not target a specific RBC antigen but may react with a broad range of different red blood cell antigen types, including the patient's own. These types of antibodies can occur in association with autoimmune disorders, lymphomas and chronic lymphocytic leukemia, certain viral or mycoplasma infections, and some medications.

An RBC antibody can occasionally be missed with antibody identification testing. There are many RBC antigens and some of them are quite rare. Testing evaluates the most common and clinically significant ones. An example of when this might occur is with a person who receives multiple recurrent transfusions and may have a variety of clinically significant and insignificant RBC antibodies. This is why the crossmatching process is important. It evaluates the compatibility of the donor's red blood cells and recipient's serum for each unit of RBCs transfused (see Blood Banking).