Antiglobulin Tests Health Article

Preparation

No preparation is needed for this test. Prior to performing the venipuncture, the nurse or other health care professional should document any medications the patient is currently taking, since many medications have been implicated in autoimmune hemolytic anemia.

Aftercare

The patient may feel discomfort when blood is drawn from a vein. Bruising may occur at the puncture site or the person may feel dizzy or faint. Pressure should be applied to the puncture site until the bleeding stops to reduce bruising. Warm packs can also be placed over the puncture site to relieve discomfort.

Complications

The most common complication is a bruise at the site of the puncture or excessive bleeding. The patient can apply moist warm compresses if there is any discomfort.

Results

Antiglobulin tests are reported as negative or positive. If the direct antiglobulin test is positive, an elution study may be performed to identify the specificity of the antibody. In addition, the indirect antiglobulin test may be performed to determine if there is unattached circulating antibody. If the indirect antiglobulin test is positive, serial dilutions may be performed to quantify the concentration of antibody. The antibody titre is defined as the highest dilution of the serum that gives a positive test result. If the antiglobulin tests are negative, the anemia is unlikely to be immune-mediated, and the physician will have to search elsewhere for a cause.

Health care team roles

A physician will order the tests, and will interpret the results. The blood specimen is drawn by a nurse or phlebotomist, and transported to the laboratory. AHG tests are performed by clinical laboratory scientists/medical technologists. If a direct AHG test is performed on tissue, the specimen is processed by a histologic technician and the tissue is examined under the microscope by a pathologist. The pathologist writes an interpretative report of the microscopic finding.

KEY TERMS

Anemia—Reduced oxygen-carrying capacity of the blood, due to too little hemoglobin or too few red blood cells.

Antibody—A protein made by the immune system, that is directed against antigens, and used as a weapon against foreign invaders in the body.

Antigen—The chemical that stimulates an immune response.

Collagen-vascular disease—Various diseases inflaming and destroying connective tissue.

Hematologist—Physician who specializes in diseases of the blood.

Hemoglobin—The red pigment in blood that carries oxygen.

Hemolysis—Breaking apart red blood cells.

Rh—A blood typing group, like the ABO system. When a mother is Rh negative and her baby is Rh positive, she may develop antibodies to the baby's blood that will cause it to hemolyze.

BOOKS

American Association of Blood Banks. Technical Manual, 13th ed., Bethesda, MD: American Association of Blood Banks, 1999.

American Society of Clinical Pathologists. Practical Diagnosis of Hematologic Disorders, 3rd ed., edited by Carl Kjeldsberg, et al. Chicago, IL: ASCP Press, 2000.

Henry, John B. Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Philadelphia, PA: W. B. Saunders, 2001.

Rosse, Wendell and H. Franklin Bunn. "Hemolytic Anemias and Acute Blood Loss." In Harrison's Principles of Internal Medicine, edited by Kurt Isselbacher, et al. New York: McGraw-Hill, 1998.

Mark A. Best