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
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. (The tube is first warmed to normal body temperature - 98.6 degrees F). The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
The sample is sent to a laboratory.
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, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
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
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
The presence of warm agglutinins may occur with:
- Infections, including brucellosis, rickettsial disease, salmonella infection, and tularemia
- Systemic lupus erythematosus
- Use of certain medicines, including methyldopa, penicillin, and quinidine
The presence of cold agglutinins may occur with:
- Infections, especially Mycoplasma pneumonia
- Previous viral, staphylococcal, or malaria infection
- Cancer, including lymphoma and multiple myeloma
- Systemic lupus erythematosus
What the risks are
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, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 164.
Baum SG. Mycoplasma infections. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 338.
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.
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; George F Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.