The complement fixation test to C. burnetii is used to detect the presence of antibodies to Coxiella burnetii (C. burnetii) bacteria in the blood. These highly infectious bacteria cause Q fever.
How the test is performed
Antibodies defend the body against some 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 bacteria or virus tells the health care provider that you had 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 attach to the antigen. This combination activates or "fixes" complement.
The test specifically looks for the antibodies to C. burnetii in the clear liquid portion of the blood called the serum. (The term for this technique is serology.) If you have persistently high levels of antibodies to C. Burnetii, you could have chronic Q fever.
How to prepare for the test
No special preparation is necessary for this test.
How the test will feel
You may feel moderate pain when the needle is inserted, or only a prick or stinging sensation. Afterward, there may be some throbbing.
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:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Marrie TJ, Raoult D. Coxiella burnetti (Q fever). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 189.Raoult D. Rickettsioses. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier. 2007:chap 348.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; 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.