Coccidioides complement fixation
Coccidioides complement fixation is a blood test that looks for antibodies to the fungus Coccidioides immitis. This fungus causes the disease coccidioidomycosis.
Coccidioides antibody test
How the test is performed
Blood is typically 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 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 in 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 complement fixation test looks at the clear liquid portion of the blood, called serum, to see if the body has produced antibodies to a specific antigen -- in this case Coccidioides immitis. If the antibodies are present, they stick, or "fix" themselves to the antigen. That is why the test is called "fixation."
How to prepare for the test
There is no special preparation for the test.
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 used to detect infection with the fungus that causes coccidioidomycosis. This condition can cause lung or widespread (disseminated) infection.
No Coccidioides immitis antibodies are detected.
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
Abnormal results mean that Coccidioides immitis antibodies are present. This can mean that you have a current or past infection.
The test may be repeated after several weeks to detect a rise in titer (antibody concentration), which confirms an active infection.
In general, the worse the infection, the higher the titer, except in people with a weakened immune system.
There can be false positive tests in patients with other fungal diseases such as histoplasmosis and blastomycosis, and false negative tests in people with single lung masses from coccidioidomycosis.
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)
Galgiani JN. Coccidioidomycosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. Philadelphia, Pa: Saunders Elsevier;2007:chap 354.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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