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Red Blood Cell Antibody Identification

Also known as: Alloantibody Identification; Antibody ID, RBC; Ab ID
Formal name: Red Blood Cell Antibody Identification
Related tests: Direct Antiglobulin; Indirect Antiglobulin; Blood Typing; Type and screen; Crossmatch

At a Glance

Why Get Tested?

To identify the specific antibody present when a direct antiglobulin test (DAT) or indirect antiglobulin test (IAT) is positive; to help identify the cause of a transfusion reaction or the cause of hemolytic disease of the newborn (HDN)

When to Get Tested?

When an IAT screening test is positive when performed as part of a prenatal workup or prior to a blood transfusion; when a person has a positive DAT following a suspected transfusion reaction or is suspected to have an autoimmune hemolytic anemia; when a newborn has HDN

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Antibodies to red blood cells (RBCs) can be produced by the body's immune system in response to being exposed to "foreign" RBC antigens, structures found on the surfaces of RBCs. This test identifies the specificity of red blood cell antibodies in the blood that were produced in response to a previous exposure to someone else's RBCs either through blood transfusion or prior pregnancy. It is often done as a follow up to a positive screening result by an indirect antiglobulin test (IAT) or when an antibody is detected attached to a patient's RBCs by a positive direct antiglobulin test (DAT).

The type of RBC antibodies that you may produce depends on the specific combination of surface antigens on your RBCs that you inherited from your parents. Normally your body will only produce antibodies directed against antigens not found on your own cells. The major RBC antigens are A, B and the Rh factor (D antigen). They determine a person's basic blood type (for more on this, see Blood Type and Blood Banking).

Our bodies naturally produce antibodies against the A and B antigens that we do not have on our red blood cells. For example, a person who is blood type A will have antibodies directed against B antigens and someone who is blood type B will have anti-A antibodies. A person who has blood type O lacks both of the A and B antigens on their red blood cells and will produce antibodies to both A and B antigens. Anti-A and anti-B antibodies are usually capable of rapidly hemolyzing red blood cells containing A or B antigens.

The Rh factor (D antigen) is a potent stimulus for antibody production. It is estimated that if an Rh negative person is exposed to only one or two drops of Rh positive blood, their immune system can be triggered to begin producing anti-D antibodies. For these reasons, blood that is to be transfused must be compatible with a person's ABO and Rh blood type; all blood donors and transfusion recipients are tested for ABO group and Rh type, and donated blood is only given to transfusion recipients of the same group and type.

 

Individual's ABO blood type Naturally occurring RBC antibodies
O Anti-A and anti-B
A Anti-B
B Anti-A
AB None

In addition to these major ABO and Rh blood group antigens, there are numerous other minor RBC blood group antigens, such as Kell, Kidd, Duffy, and other Rh antigens. Antibodies to these antigens are not made naturally and are only produced by the body when exposed to them through blood transfusion or when a mother is exposed to a baby's blood cells during pregnancy.

When a person with a RBC antibody is again exposed to RBCs bearing the "foreign" antigen, whether by another transfusion or pregnancy, the RBC antibodies may attach to the specific antigens on the foreign RBCs and target the RBCs for destruction. Depending on the antigen and antibody involved and the quantity of RBCs affected, this can cause a reaction ranging from mild to severe and potentially life-threatening. It may happen immediately, such as during a blood transfusion, or take longer, from one to several days following a transfusion. When antibodies attach to antigens, the red blood cells can be destroyed, termed hemolysis. This can occur within the blood vessels or in the liver or spleen and cause symptoms and signs such as fever, chills, nausea, flank pain, low blood pressure, bloody urine, and jaundice.

Antibody identification tests that detect antibodies directed against the minor RBC blood group antigens are not routinely done but are performed when the presence of an antibody is detected through a positive IAT or DAT.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

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.

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When is it ordered?

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.

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What does the test result mean?

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)      

 

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Is there anything else I should know?

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).

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Common Questions

1.  Should everyone have an IAT performed?

It is not generally necessary unless someone is pregnant or receiving a transfusion. RBC antibodies do not otherwise affect the health of someone who has them. Sometimes a doctor may test a woman after a pregnancy, especially if her baby had complications, to determine if there may be risks associated with a future pregnancy. Or they may test a person who has received recurrent transfusions to evaluate which RBC antibodies have developed since the last time the person was tested.

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2.  Do RBC antibodies go away?

No. They may drop to low levels in the blood but once you have them, your body will keep a "library" of them so that they can be produced as needed.

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3.  Do RBC antibodies affect blood donation?

They do not affect the safety of the person donating and will not affect the processing of red blood cells for transfusion. If someone has potent RBC antibodies in their plasma, however, then that plasma may not be acceptable for all transfusions.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

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