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. 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. This complement fixation test 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." The test specifically looks for the antibodies in the clear liquid portion of the blood called the serum. The general term for such a technique is called serology. There are several other serology techniques that can be used depending on the suspected antibodies. They include agglutination and enzyme immunoassay.
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