Blood Typing

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Formal name: ABO Grouping and Rh Typing
Related tests: Direct Antiglobulin Test, Indirect Antiglobulin Test, Compatibility Testing, Crossmatch, Antibody Identification; HLA Testing

At a Glance

Why Get Tested?

To determine ABO blood group and Rh type

When to Get Tested?

When you need to be transfused with blood or blood components or when you donate blood at a collection facility; pregnant women are tested to determine the risk of Rh incompatibility between the mother and fetus

Sample Required?

A blood sample drawn from a vein in your arm or from a heelstick in the case of an infant

Test Preparation Needed?

None

The Test Sample

What is being tested?

Red blood cells (RBCs) have markers or antigens on the surface of the cells. Two major antigens or surface identifiers on human RBCs are the A and B antigens. Blood is grouped according to the presence or absence of these antigens. People whose red blood cells have A antigens are considered to be blood group A; those with B antigens are group B; those with both A and B antigens are group AB; and those who do not have either of these markers are considered to have blood group O. Another important surface antigen is called Rh factor. If it 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 we do not have on our red blood cells. For example, a person who is blood type A will have antibodies directed against the B antigens on red blood cells and someone who is type B will have anti-A antibodies and so on.

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

a person with bloodtype ... 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 ABO group and are significant in defining the types of blood that they can safely receive. 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, the 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.

How is the sample collected for testing?

A sample of blood is drawn from a vein in your arm or from the tip of your 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

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.

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.