The Test Sample
What is being tested?
Red blood cell antibodies are proteins produced by the body's immune system directed against "foreign" red blood cells (RBCs). This test identifies the specific red blood cell antibodies present in the blood of an individual who has a positive screening test for RBC antibodies (an RBC antibody screen or direct antiglobulin test, DAT).
Each individual inherits a specific combination of RBC antigens, structures found on the surface of the cells, including those associated with the major blood types A, B, AB, and O. Normally, people will only produce antibodies directed against "foreign" antigens not found on their own cells. All individuals naturally produce antibodies against the A and/or B antigens that are not on their own RBCs. For example, a person who is blood type A will have antibodies in their blood to the B antigen.
Another important RBC antigen is an Rh antigen called the D antigen. People either have the D antigen on their RBCs (Rh-positive) or do not (Rh-negative). Antibodies to the D antigen are not naturally-occurring; a person who is Rh-negative produces antibodies only after being exposed to RBCs from another person that has the D antigen, for example, a mother exposed to her baby's RBCs during pregnancy or during a blood transfusion.
Blood that is to be transfused must be compatible with the recipient's ABO and Rh blood type because ABO and Rh antibodies present in the recipient's blood have the potential to rapidly destroy (hemolyze) the transfused RBCs and cause serious complications. Antibodies to the major blood types are routinely identified using blood typing tests and blood for transfusion is matched with the ABO and Rh blood type of the recipient. (For more on this, see Blood Typing and Blood Banking.)
In addition to these ABO and Rh blood group antigens, there are numerous other 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, labor and delivery. These antibodies may or may not be associated with adverse reactions, and identification of the specific type of RBC antibody present in a person's blood may be important in avoiding these reactions.
Antibody identification tests that classify antibodies directed against RBC antigens other than ABO are performed when the presence of an antibody is detected through a positive antibody screen (DAT or RBC antibody screen). This screen may be done as part of a "type and screen," which is ordered in situations such as:
- Part of a prenatal workup
- When a blood transfusion has been ordered
- Following a suspected transfusion reaction
- Hemolytic disease of the newborn (HDN)
- Suspected autoimmune hemolytic anemia (in which the body inappropriately makes antibodies against antigens on its own red blood cells)
Complications can develop when a person with an 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 them 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. Antibody/antigen combinations capable of causing RBC destruction are called clinically significant. The reaction may happen immediately, such as during a blood transfusion, or take longer, from one to several days or longer following a transfusion. When antibodies attach to antigens, the red blood cells can be destroyed, called hemolysis. This can occur within the blood vessels or in the liver or spleen. Hemolysis can cause symptoms and signs such as fever, chills, nausea, flank pain, low blood pressure, bloody urine, and jaundice.
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.