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Complement Fixation Test for C. Burnetii

Definition

This test is used to detect the presence of antibodies to Coxiella burnetii (C. burnetii) bacteria in the blood. This highly infectious bacteria causes Q fever.

How the test is performed

Antibodies defend the body against bacteria, viruses, fungi, and other foreign substances, called antigens. Certain cells cause the body to produce antibodies during an active infection.

When you first become sick, few antibodies may be detected. Antibody production increases during the course of an infection. Antibody tests are often repeated several weeks after the first test is done, so that a comparison can be made to the first test. A rising level of antibody to a specific infectious agent tells the health care provider that you have an active infection.

The complement fixation test looks to see if the body has produced antibodies to a specific antigen -- in this case, the C.burnetii bacteria. 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 to C. burnetii in the clear liquid portion of the blood called the serum. (The general term for such a technique is called serology.) If you have consistently high levels of antibodies to C. Burnetii, this indicates chronic Q fever.

How to prepare for the test

No special preparation is necessary for this test.

How the test will feel

A needle is inserted to draw blood. You may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

The test is performed to detect Q fever.

Normal Values

The absence of antibodies to C. burnetii is normal.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results

What abnormal results mean

An abnormal result means you have a current infection with C. burnetii, or that you have been exposed to the bacteria in the past. People with past exposure may have antibodies, even if they are not aware that they were exposed. Further testing may be needed to distinguish between current, previous, and chronic infection.

What the risks are

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.

Other risks associated with having blood drawn are slight but may include:

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

References

Raoult D. Rickettsioses. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier. 2007: chap 348.

Review Date: 5/30/2009

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