How the Test is Performed

Complement fixation is a specific laboratory technique that looks to see if the body has produced antibodies to a specific foreign substance (antigen) -- in this case Coccidioides immitis. If the antibodies are present, they stick, or "fix" themselves, to the antigen. That's why the test is called "fixation."

The spinal fluid needed to perform this test is usually obtained by lumbar puncture (spinal tap).

How to Prepare for the Test

A consent form must be signed. You will need to remain in the hospital for about 8 hours afterwards, and you should remain lying flat.

How the Test Will Feel

See: Lumbar puncture

Why the Test is Performed

Complement fixation is the most sensitive test for the fungus Coccidioides immitis.

Normal Results

The absence of fungus (a negative test) is normal.

What Abnormal Results Mean

If the test is positive for fungus, the results indicate an active infection in the central nervous system. (See: Disseminated coccidioidomycosis ).

Risks

See: Lumbar puncture

Considerations

In some cases, this test may be done as a blood test. See also: Coccidioides complement fixation.

In the initial stage of an illness, few antibodies may be detected. Antibody production increases during the course of an infection. For this reason, such tests are often repeated several weeks after the first test is done.

Note: While an abnormal result on the spinal fluid test specifically means that the central nervous system is infected, an abnormal result on the blood test does not pinpoint the exact area of infection. It only means that there is a coccidioides infection somewhere in the body.

Alternative Names

Coccidioides antibody test - spinal fluid

References

Galgiani JN. Coccidioidomycosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 354.

Update Date: 5/30/2012

Reviewed by: 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.