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Blood Typing

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Also known as: Blood Group; Rh Factor
Formal name: ABO Group and Rh Type
Related tests: Direct Antiglobulin Test, RBC Antibody Screen, Compatibility Testing, Crossmatch, RBC Antibody Identification, HLA Testing

At a Glance

Why Get Tested?

To determine your ABO blood group and Rh type

When to Get Tested?

When you need a transfusion of blood or blood components; when you donate blood at a collection facility or donate an organ, tissue, or bone marrow for transplantation; before or during a woman's pregnancy to determine the risk of Rh incompatibility with the fetus

Sample Required?

A blood sample drawn from a vein in your arm or, for infants, from a heelstick

Test Preparation Needed?

None

The Test Sample

What is being tested?

Blood types are based on the markers (specific carbohydrates or proteins) or antigens on the surface of red blood cells (RBCs). Two major antigens or surface identifiers on human RBCs are the A and B antigens. Another important surface antigen is called Rh. Blood typing detects the presence or absence of these antigens to determine a person's ABO blood group and Rh type.

People whose red blood cells have A antigens are in blood group A, those with B antigens are group B, those with both A and B antigens are in group AB, and those who do not have either of these markers are in blood group O.

If the Rh protein is present on the red blood cells, a person's blood type is Rh+ (positive); if it is absent, the person's blood is type Rh- (negative).

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 anti-B antibodies directed against the B antigens on red blood cells and someone who is type B will have anti-A antibodies directed against the A antigens. People with type AB blood have neither of these antibodies, while those with type O blood have both.

The following table indicates the type of antibodies a person is expected to have based on their blood type.

a person with blood type ... will have antibodies to ...
A B antigen
B A antigen
AB Neither antigen
O
A and B antigens

These antibodies are useful for determining a person's blood type and help determine the types of blood that he or she can safely receive (compatibility). If a person who is group A with antibodies directed against the B antigen, for example, were to be transfused with blood that is type B, his or her own antibodies would target and destroy the transfused red blood cells, causing severe, potentially fatal complications. Thus, it is critical to match a person's blood type with the blood that is to be transfused.

Unlike antibodies to A and B antigens, antibodies to Rh are not produced naturally. That is, Rh antibodies develop only after a person who does not have Rh factor on his or her red blood cells (Rh negative) is exposed to Rh positive red blood cells. This can happen during pregnancy or birth when an Rh-negative woman is pregnant with an Rh-positive baby, or sometimes when an Rh-negative person is transfused with Rh-positive blood. In either case, the first exposure to the Rh antigen may not result in a strong response against the Rh positive cells, but subsequent exposures may cause severe reactions.

How is the sample collected for testing?

A sample of blood is drawn from a vein in the arm or from the tip of the finger (fingerstick). In newborns, blood from the umbilical cord or a small amount of blood from a heelstick may be used for testing.

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 special preparation is needed for this test.

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

Blood Types. American Red Cross. Available online at http://www.redcrossblood.org/learn-about-blood/blood-types through http://www.redcrossblood.org. Copyright 2014. Accessed October 24, 2014.

Testing and Procedures: Blood Transfusion. Mayo Clinic. Available online at http://www.mayoclinic.org/tests-procedures/blood-transfusion/basics/risks/prc-20021256 through http://www.mayoclinic.org. Last updated April 26, 2012. Accessed October 24, 2014.

Rare Donor Program. Lifeshare Blood Centers. Available online at http://www.lifeshare.org/services/rare-donor-program through http://www.lifeshare.org. Copyright 2014. Accessed October 27, 2014.

Blood Types: Distribution Stats, Interesting Facts. Blood Banker. Available online at http://bloodbanker.com/plasma/plasma-donation/blood-donation-terms/ through http://bloodbanker.com. Accessed October 28, 2014.

(Updated Oct 29, 2014) Gonsorcik V. ABO Grouping. Medscape Reference. Available online at http://emedicine.medscape.com/article/1731198-overview through http://emedicine.medscape.com. Accessed October 2014.

(Updated Nov 6, 2013) Gonsorcik V. Rh Typing. Medscape Reference. Available online at http://emedicine.medscape.com/article/1731214-overview through http://emedicine.medscape.com. Accessed October 2014.

Sources Used in Previous Reviews

Pagana, Kathleen D. & Pagana, Timothy J. (© 2006). Mosby's Manual of Diagnostic and Laboratory Test 3rd Edition: Mosby, Elsevier, Saint Louis, MO., Pp. 141-145.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Ch. 34.

Medline Plus Medical Encyclopedia. Blood Typing (Online information, accessed October 2007). Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003345.htm.

(September 2007) National Heart, Lung and Blood Institute. Diseases and Conditions Index: Blood Transfusion (Online information). Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/bt/bt_whatis.html through http://www.nhlbi.nih.gov. Accessed November 2007.

(June 2005) Nemours Foundation. Kids Health: What You Need to Know in an Emergency (Online information). Available online at http://kidshealth.org/parent/firstaid_safe/home/healthin.html through http://kidshealth.org. Accessed October 2007.

(July 2007) AABB. About Blood and Cellular Therapies: Blood FAQ (Online information). Available online at http://www.aabb.org/Content/About_Blood/FAQ/bloodfaq.htm through http://www.aabb.org. Accessed October 2007.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Ch. 34.

(February 5, 2010) Medline Plus Medical Encyclopedia: Blood Typing (Online information). Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003345.htm. Accessed July 2011.

(July September 20097) National Heart, Lung and Blood Institute. Diseases and Conditions Index. Blood Transfusion (Online information). Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/bt/bt_whatis.html through http://www.nhlbi.nih.gov. Accessed July 2011.

(©2011July 2007) AABB. About Blood and Cellular Therapies: Blood FAQ. Available online at http://www.aabb.org/Content/About_Blood/FAQ/bloodfaq.htm through http://www.aabb.org. Accessed July 2011.

(©2011) National American Red Cross. Learn About Blood. Available online at http://www.redcrossblood.org/learn-about-blood through http://www.redcrossblood.org. Accessed July 2011.

(November 20, 2009) Sandler G. Transfusion Reactions. Medscape Reference. Available online at http://emedicine.medscape.com/article/206885-overview through http://emedicine.medscape.com. Accessed July 2011.

(November 4, 2009) Salem L. Rh Incompatibility. Medscape Reference. Available online at http://emedicine.medscape.com/article/797150-overview through http://emedicine.medscape.com. Accessed July 2011.

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