Coccidioides complement fixation

A blood sample is needed.

There is no special preparation for the test.

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.

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.

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.

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.

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)

Coccidioides antibody test; Coccidioidomycosis blood test

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.

Updated by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.