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RBC Antibody Identification

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

At a Glance

Why Get Tested?

To identify the specific antibody detected by a direct antiglobulin test (DAT) or RBC antibody screen; to help identify the cause of a transfusion reaction, hemolytic disease of the newborn (HDN), or hemolytic anemia

When to Get Tested?

When a DAT or RBC antibody screen is positive; when a transfusion reaction is susptected or when a newborn has HDN

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


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.

The Test

Common Questions

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Article Sources

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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.

Sources Used in Current Review

Oren, E. and Sepulveda, J. (Updated 2012 January 3). Alloimmunization From Transfusions. Medscape Reference [On-line information]. Available online at through Accessed November 2012.

Goodell, P. et. al. (2010) Risk of Hemolytic Transfusion Reactions Following Emergency-Release RBC Transfusion. American Journal of Clinical Pathology v 134. [On-line information]. Available online at through Accessed November 2012.

Arraut, A. and Tran, S. (Updated 2011 July 22). Erythrocyte Alloimmunization and Pregnancy. Medscape Reference [On-line information]. Available online at through Accessed November 2012.

Yazdanbakhsh, K. et. al. (2012 July 19). Red blood cell alloimmunization in sickle cell disease: pathophysiology, risk factors, and transfusion management. Blood v 120 (3) [On-line information]. Available online at through Accessed November 2012.

(© 1995-2012). Antibody Screen, Erythrocytes. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at through Accessed November 2012.

(Revised 2011). Blood Transfusion. Leukemia & Lymphoma Society [On-line information]. PDF available for download through Accessed November 2012.

Brooks, M. (2012 May 22). Risk of Transfusion-Induced Alloimmunization High in IBD Patients. Medscape Today News from Reuters Health Information [On-line information]. Available online at through Accessed November 2012.

Sources Used in Previous Reviews

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 122-123.

Taylor, C. (2008 November 25). Immunological Complications of Blood Transfusion. Medscape Today from Transfusion Alternatives in Transfusion Medicine [On-line information]. Available online at through Accessed June 2009.

Boucher, B. and Hannon, T. (2007 October 29). Blood Management: A Primer for Clinicians. Medscape Today from Pharmacotherapy [On-line information]. Available online at through Accessed June 2009.

Dean, L. (2008 February 25). Blood Groups and Blood Cell Antigens. National Center for Biotechnology Information [On-line information]. Available online at through Accessed June 2009.

Dugdale III, D. (Updated 2009 March 02). Transfusion Reaction - hemolytic. MedlinePlus Medical Encyclopedia [On-line information]. Available online at Accessed June 2009.

(© 2006-2008). Transfusion, Compatibility Testing. ClinLab Navigator [On-line information]. Available online at through Accessed June 2009.

(Revised 1999 January). The Use of Human Blood and Blood Components. American Red Cross, Education Circular of Information [On-line information]. Available online at through Accessed June 2009.