Coccidioides antibody test

Alternative names
Coccidioides complement fixation

Definition
Coccidioides complement fixation is a test to determine the presence of antibodies to the fungus coccidioidomycosis by a specific serologic technique.

How the test is performed

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Serology refers to the study of serum (the fluid portion of blood) for its antibody content. An antibody defends the body against bacteria, viruses, fungus, or other foreign bodies (antigens). Certain microbial cells stimulate the body to produce these antibodies during an active infection. Antibody production increases during the course of an infection.

In the initial stage of an illness, few antibodies may be detected. For this reason, serology tests are often repeated 10 days to 2 weeks after the initial sample. In the laboratory, the antibodies react with antigens in specific ways that can be used to confirm the identity of a specific microorganism.

There are several serology techniques that can be used depending on the suspected antibodies. Serology techniques include agglutination, precipitation, complement-fixation, fluorescent antibodies, and others.

How to prepare for the test
There is no special preparation for the test.

For infants and children:
The preparation you can provide for this test depends on your child’s age and experience. For specific information regarding how you can prepare your child, see the following topics:

     
  • Infant test or procedure preparation (birth to 1 year)  
  • Toddler test or procedure preparation (1 to 3 years)  
  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

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 coccidioidomycosis, which can cause lung or widespread (disseminated) infection.

Normal Values
No coccidioides antibodies are detected.

What abnormal results mean

Abnormal results indicate that coccidioides antibodies are present. This can indicate a current or prior infection. The test may be repeated after several weeks to detect a rise in titer (antibody count), which helps to confirm an active infection. Titers greater than 1:16 usually indicate active infection (that is, a count of 1:32 or higher).

In general, the worse the infection, the higher the titer, except in patients with weakened immune systems.

There can be false positive tests in patients with the fungal disease histoplasmosis, and false negative tests in patients with only solitary lung masses from coccidioidomycosis.

What the risks are

The risks associated with having blood drawn are:

     
  • Excessive bleeding  
  • Fainting or feeling light-headed  
  • Hematoma (blood accumulating under the skin)  
  • Infection (a slight risk any time the skin is broken)  
  • Multiple punctures to locate veins

Special considerations
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.

Johns Hopkins patient information

Last revised: December 6, 2012
by Dave R. Roger, M.D.

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