Coccidioides complement fixation

Definition

Coccidioides complement fixation is a blood test that looks for substances (proteins) called antibodies, which are produced by the body in reaction to the fungus Coccidioides immitis. This fungus causes the disease coccidioidomycosis.

Alternative Names

Coccidioides antibody test; Coccidioidomycosis blood test

How the Test is Performed

A blood sample is needed.

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. Afterward, there may be some throbbing.

Why the Test is Performed

This test is used to detect infection with the fungus that causes coccidioidomycosis, or Valley fever. This condition can cause lung (localized) or widespread (disseminated) infection.

Normal Results

A normal result means no Coccidioides immitis antibodies are detected in the blood sample.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your health care provider 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 is the titer, except in people with a weakened immune system.

There can be false positive tests in people with other fungal diseases such as histoplasmosis and blastomycosis, and false negative tests in people with single lung masses from coccidioidomycosis.

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood 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 lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Galgiani JN. Coccidioidomycosis (Coccidioides species). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 265.

Iwen PC, Thompson GR, Wiederhold NP. Mycotic diseases. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 60.