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Alternative namesCold agglutinins; Weil-Felix reaction; Widal's test
DefinitionThis test measures the level of warm or cold agglutinins in blood. Agglutinins are antibodies that cause the red blood cells to gather together. Cold agglutinins are active at cold temperatures. Warm agglutinins are active at normal body temperature.
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 puncture site is cleaned with antiseptic, and an elastic band or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
How to prepare for the testThere is no special preparation.
Infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following:
How the test will feelWhen 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 performedThese antibodies can cause a hemolytic anemia. This occurs when the body destroys its own red blood cells. Distinguishing between warm and cold agglutinins can help understand why the hemolytic anemia is occuring and directs therapy.
What abnormal results mean
Elevated levels of cold or warm agglutinins can cause hemolytic anemia. Some patients with moderately elevated levels will have no hemolysis and likely won't require therapy.
The presence of warm agglutinins may occur with:
The presence of cold agglutinins may occur with:
What the risks are
Special considerationsIf cold agglutinin disease is suspected, the individual needs to be kept warm.
Update Date: 9/11/2003Megan E. B. Clowse, M.D., M.P.H., Division of Rheumatology, Johns Hopkins Hospital, Baltimore, MD. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT