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Febrile/cold agglutinins

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 describes the blood test that is used to measure the level of these antibodies in the blood.

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

There is no special preparation.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing where the needle was inserted.

Why the Test is Performed

This test is done to diagnose certain infections and find the cause of hemolytic anemia (a type of anemia that occurs when red blood cells are destroyed). Knowing whether there are warm or cold agglutinins can help explain why the hemolytic anemia is occurring and direct treatment.

Normal Results

  • 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.

What Abnormal Results Mean

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

Warm agglutinins may occur with:

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 a disease linked to cold agglutinin is suspected, the person needs to be kept warm.

Alternative Names

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



Baum SG. Mycoplasma infections. In: Goldman L, Schafer AI, eds.Goldman's Cecil Medicine

Jäger U, Lechner. Autoimmune hemolytic anemia. In: Hoffman R, Benz EJ Jr., Silberstein LE, et al, eds.Hematology: Basic Principles and Practice

Schwartz RS. Autoimmune and intravascular hemolytic anemias. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine

Update Date 5/15/2014

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