CSF coccidioides complement fixation

Definition

CSF coccidioides complement fixation looks for antibodies to the fungus Coccidioides immitis in the cerebrospinal (CSF) fluid, the fluid surrounding the brain and spine.

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 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."

An antibody defends the body against bacteria, viruses, fungus, or other foreign body ( antigen ). Certain cells tell the body to produce antibodies during an active infection.

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 should be prepared to remain in the hospital for at least the 6 - 8 hours afterwards, and you should remain lying flat.

How the test will feel

The position may be uncomfortable, but it is imperative that you remain in the curled position to avoid moving the needle and possibly injuring the spinal cord.

The scrub will feel cold and wet. The anesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted, and there is usually some brief pain when the needle goes through the meninges. This pain should stop in a few seconds. Overall, discomfort is minimal to moderate. The entire procedure usually takes about 30 minutes but may take longer, the actual pressure measurements and fluid collection only takes a few minutes.

Why the test is performed

Complement fixation is the most sensitive test for the fungus coccidioides.

Normal Values

The presence of no fungus 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 ).

What the risks are

• Risks of lumbar puncture include:
  • Hypersensitivity (allergic) reaction to the anesthetic
  • Discomfort during the test
  • Headache after the test
  • Bleeding into the spinal canal
• Brain herniation (if performed on a person with increased intracranial pressure ), resulting in brain damage and/or death
• Damage to the spinal cord (particularly if the person moves during the test)

Special considerations

This test may also 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.

Illustrations

Blood test

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Coccidioides antibody test - spinal fluid