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    Coombs’ test

    Direct antiglobulin test; Indirect antiglobulin test

    The Coombs' test looks for antibodies that may stick to your red blood cells and cause red blood cells to die too early.

    How the Test is Performed

    A blood sample is needed. For information on how this is done, see: Venipuncture

    How to Prepare for the Test

    No special preparation is necessary for this test.

    How the Test Will Feel

    When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a bruise may develop at the site where the needle was inserted.

    Why the Test is Performed

    There are two types of the Coombs' test:

    • Direct
    • Indirect

    The direct Coombs' test is used to detect antibodies that are stuck to the surface of red blood cells. Many diseases and drugs (including quinidine, methyldopa, and procainamide) can cause this. These antibodies sometimes destroy red blood cells and cause anemia. Your doctor may order this test if you have signs or symptoms ofanemia or jaundice.

    The indirect Coombs' test looks for free-flowing antibodies against certain red blood cells. It is is most often done to determine if you may have a reaction to a blood transfusion.

    Normal Results

    A normal result means there were no clumping of cells (agglutination), meaning you have no antibodies to red blood cells.

    Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

    What Abnormal Results Mean

    An abnormal (positive) direct Coombs' test means you have antibodies that act against your red blood cells. This may be due to:

    • Autoimmune hemolytic anemia
    • Chronic lymphocytic leukemia or similar disorder
    • Drug-induced hemolytic anemia
    • Erythroblastosis fetalis (hemolytic disease of the newborn)
    • Infectious mononucleosis
    • Mycoplasmal infection
    • Syphilis
    • Systemic lupus erythematosus
    • Transfusion reaction, such as one due to improperly matched units of blood

    The test may also be abnormal without any clear cause, especially among the elderly.

    An abnormal (positive) indirect Coombs' test means you have antibodies that will act against red blood cells your body views as foreign. This may suggest:

    • Autoimmune or drug-induced hemolytic anemia
    • Erythroblastosis fetalis hemolytic disease
    • Incompatible blood match (when used in blood banks)

    Risks

    Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

    Other risks associated with having blood drawn are slight but may include:

    • Excessive bleeding
    • Fainting or feeling light-headed
    • Hematoma (blood accumulating under the skin)
    • Infection (a slight risk any time the skin is broken)

    References

    Powers A, Silberstein LE. Autoimmune hemolytic anemia. In: Hoffman R, Benz EJ Jr., Shattil SS, et al., eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingston Elsevier; 2008: chap 47.

    Schrier SL, Price EA. Extrinsic nonimmune hemolytic anemias. In: Hoffman R, Benz EJ Jr., Shattil SS, et al., eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingston Elsevier; 2008: chap 48.

    Schwartz RS. Autoimmune and intravascular hemolytic anemias In: Goldman L, Schafer AI, eds.Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 163.

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            Tests for Coombs’ test

            Review Date: 2/12/2012

            Reviewed By: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

            The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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