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Agglutinins are antibodies that cause the red blood cells to clump together.

• Cold agglutinins are active at cold temperatures.
• Febrile (warm) agglutinins are active at normal body temperatures.

This article discusses the blood test used to measure the level of these antibodies in the blood.

Cold agglutinins; Weil-Felix reaction; Widal's test; Warm agglutinins; Agglutinins

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

There is no special preparation.

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.

This test is done to diagnose certain infections and to determine the cause of hemolytic anemia. Distinguishing between warm and cold agglutinins can help understand why the hemolytic anemia is occurring and can direct therapy.

• Warm agglutinins: no agglutination in titers at or below 1:80
• Cold agglutinins: no agglutination in titers at or below 1:16

The examples above are common measurements for results of these tests. 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.

An abnormal (positive) result means there were agglutinins in the blood sample.

Warm agglutinins may occur with:

• Infections, including brucellosis, rickettsial disease, salmonella infection, and tularemia
• Lymphoma
• Systemic lupus erythematosus
• Use of certain medicines, including methyldopa, penicillin, and quinidine

Cold agglutinins may occur with:

• Infections, especially mononucleous and Mycoplasma pneumonia
• Chicken pox (varicella)
• Cytomegalovirus infection
• Cancer, including lymphoma and multiple myeloma
• Listeria monocytogenes
• Systemic lupus erythematosus
• Waldenstrom macrogolulinemia

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)

If cold agglutinin disease is suspected, the individual needs to be kept warm.

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

Baum SG. Mycoplasma infections. In: Goldman L, Schafer AI,eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 325.

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