Febrile/cold agglutinins; Weil-Felix reaction; Widal’s test
This 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.
In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
The sample is collected in a tube that has been warmed to normal body temperature (98.6 degrees F) and sent to a laboratory.
How to prepare for the test
There 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:
- infant test or procedure preparation (birth to 1 year)
- toddler test or procedure preparation (1 to 3 years)
- preschooler test or procedure preparation (3 to 6 years)
- schoolage test or procedure preparation (6 to 12 years)
- adolescent test or procedure preparation (12 to 18 years)
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
These 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.
- Warm agglutinins: no agglutination in titers at or below 1:80
- Cold agglutinins: no agglutination in titers at or below 1:16
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:
- Infections, including brucellosis, rickettsial disease, salmonella infection, and tularemia
- Systemic lupus erythematosus
- Medications, including methyldopa, penicillin, and quinidine
The presence of cold agglutinins may occur with:
- Infections, especially Mycoplasma pneumonia. Also after viral, staphylococcal, and malaria infection.
- Cancer, including lymphoma and multiple myeloma
- Systemic lupus erythematosus
What the risks are
- excessive bleeding
- fainting or feeling light-headed
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
If cold agglutinin disease is suspected, the individual needs to be kept warm.
by Dave R. Roger, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.