Red Blood Cell (RBC) Antibody Screen
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- Also Known As:
- RBC Antibody Screen
- Indirect Antiglobulin Test
- IAT
- Indirect Coombs Test
- Indirect Anti-human Globulin Test
- Antibody Screen

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At a Glance
Why Get Tested?
To detect antibodies directed against red blood cell antigens
When To Get Tested?
When preparing for a blood transfusion; during pregnancy and at delivery
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
What is being tested?
The RBC antibody screen looks for circulating antibodies in the blood directed against red blood cells (RBCs). The primary reason that a person may have RBC antibodies circulating in the blood is because the person has been exposed, through blood transfusion or through pregnancy, to RBCs other than his or her own (foreign RBCs). These antibodies have the potential to cause harm if a person is transfused with red blood cells that the antibodies may target or if a pregnant woman has antibodies that target the red cells of her developing baby.
RBCs normally have structures on their surface called antigens. People have their own individual set of antigens on their RBCs, determined by inheritance from their parents. The major antigens or surface identifiers on human RBCs are the O, A, and B antigens, and a person’s blood is grouped into an A, B, AB, or O blood type according to the presence or absence of these antigens.
Another important surface antigen is Rh factor, also called D antigen. If it is present on a person’s red blood cells, that person’s blood type is Rh+ (positive); if it is absent, the blood is type Rh- (negative). (For more on these antigens, see the article on Blood Typing). In addition, there are many other types of RBC antigens that make up lesser-known blood groups, such as Kell, Lewis, and Kidd blood groups.
There are a few reasons why someone may produce antibodies against RBC antigens.
- Following blood transfusions: Antibodies directed against A and B red cell antigens are naturally-occurring; we produce them without having to be exposed to the antigens. Before receiving a blood transfusion, a person’s ABO group and Rh type are matched with that of donor blood to prevent a serious transfusion reaction from occurring. That is, the donor’s blood must be compatible with the recipient’s so that antibodies do not react with and destroy donor blood cells.If someone receives a blood transfusion, the person’s body may also recognize other RBC antigens from other blood groups (such as Kell or Kidd) that the person does not have as foreign. The recipient may produce antibodies to attack these foreign antigens. People who have many transfusions make antibodies to RBCs because they are exposed to foreign RBC antigens with each transfusion.
- During pregnancy, with blood type incompatibility between mother and baby: A baby may inherit antigens from the father that are not on the mother’s RBCs. The mother may be exposed during pregnancy or at delivery to the foreign antigens on her baby’s RBCs when some of the baby’s cells enter the mother’s circulation as the placenta separates. The mother may begin to produce antibodies against these foreign RBC antigens. This can cause hemolytic disease of the newborn, usually not affecting the first baby but affecting subsequent children when the mother’s antibodies cross the placenta, attach to the baby’s RBCs, and hemolyze them. An RBC antibody screen can help determine if the mother has produced RBC antibodies outside of the ABO blood group.
The first time a person is exposed to a foreign RBC antigen, by transfusion or pregnancy, the person may begin to produce antibodies but his or her cells do not usually have the time during the first exposure to make enough antibodies to actually destroy the foreign RBCs. When the next transfusion or pregnancy occurs, the immune response may be strong enough for enough antibodies to be produced, attach to, and break apart (hemolyze) the transfused RBCs or the baby’s RBCs. Antibodies to the ABO antigens are naturally-occurring so do not require exposure to foreign RBCs.
Common Questions
Related Content
On This Site
Tests: Direct Antiglobulin Test; Blood Typing
Articles: Transfusion Medicine
Elsewhere On The Web
March of Dimes Fact Sheet: Rh disease
AABB: Blood FAQ
Red Cross: Types of Blood Transfusions
MedlinePlus Medical Encyclopedia: Transfusion reaction – hemolytic
View Sources
Sources Used in Current Review
(March 25, 2015) Sandler, S G. Transfusion Reactions. Medscape Reference. Available online at http://emedicine.medscape.com/article/206885-overview. Accessed March 2016.
Wintrobe’s Clinical Hematology. 12th ed. Greer J, Foerster J, Rodgers G, Paraskevas F, Glader B, Arber D, Means R, eds. Philadelphia, PA: Lippincott Williams & Wilkins: 2009, Pp 682-683.
Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2011, Pp 711-714.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pgs 286-289.
Dhaliwal, G. et. al. (2004 June 1). Hemolytic Anemia. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20040601/2599.html.
Triulzi, D. (2000 October). Indirect and Direct Antiglobulin (Coombs) Testing and the Crossmatch. Transfusion Medicine Update [On-line information]. Available online at http://www.itxm.org/TMU2000/tmu10-2000.htm.
Grund, S., Updated (2004 August 16, Updated). Coombs’ test – direct. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003344.htm.
Grund, S., Updated (2004 August 16, Updated). Coombs’ test – indirect. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003343.htm.
(2001 March).Rh Disease. March of Dimes Fact Sheet [On-line information]. Available online at http://www.marchofdimes.com/professionals/681_1220.asp.
(1995-2005). Autoimmune Hemolytic Anemia. The Merck Manual of Diagnosis and Therapy. Anemias Caused By Excessive Hemolysis. [On-line information]. Available online at http://www.merck.com/mrkshared/mmanual/section11/chapter127/127d.jsp.
Suzanne H. Butch, MA, CLDir. Chief Technologist. Blood Bank and Transfusion Service. University of Michigan Hospitals and Health Centers, Ann Arbor, Michigan.
Julie Brownie MBA, CLS(NCA), SBB(ASCP). Coral Blood Services. Bangor, Maine.
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 307-308.
Wu, A. (2006).Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 126-129.
Cutler, C. (2006 September 11, Updated). Coombs’ test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003344.htm. Accessed on 10/01/08.
Sandler, S.G. and Johnson, V. (2008 September 25, Updated). Transfusion Reactions. EMedicine [On-line information]. Available online at http://www.emedicine.com/med/TOPIC2297.HTM. Accessed on 10/01/08.
Levin, M. (2007 March 13, Updated). Transfusion Reaction. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001303.htm. Accessed on 10/04/08.
(© 2008) Hemolytic Disease of the Newborn. Lucille Packard Children’s Hospital at Stanford. Available online at http://www.lpch.org/DiseaseHealthInfo/HealthLibrary/hrnewborn/hdn.html. Accessed October 2008.
Wagle, S. and Deshpande, P. (Updated 2011 May 18). Hemolytic Disease of Newborn. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/974349-overview. Accessed July 2012.
Vorvick, L. (Updated 2012 February 7). Coombs’ test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003344.htm. Accessed July 2012.
(© 1996-2012). Rh Disease. The Children’s Hospital of Philadelphia [On-line information]. Available online at http://www.chop.edu/healthinfo/rh-disease.html. Accessed July 2012.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby’s Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 309-310.
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