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Complement fixation test to C. burnetii

The complement fixation test to C. burnetii is a blood test that checks for infection due to bacterium called Coxiella burnetii (C. burnetii) which causes Q fever.

How the Test is Performed

A blood sample is drawn from a vein.

The sample is sent to a laboratory where it is examined for Coxiella antibodies using a laboratory method called complement fixation. This technique checks if the body has produced substances called antibodies to a specific foreign substance (antigen), in this case Coxiella burnetii. Antibodies defend the body against bacteria, viruses, and fungi. If the antibodies are present, they stick, or "fix" themselves, to the antigen. This is why the test is called "fixation."

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.

Why the Test is Performed

This test is done to detect Q fever.

Normal Results

Absence of antibodies to C. burnetii is normal. It means you do not have Q fever.

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.


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)


During the early stage of an illness, few antibodies may be detected. Antibody production increases during the course of an infection. For this reason, this test may be repeated several weeks after the first test.



Marrie TJ, Raoult D. Coxiella burnetti (Q fever). In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill-Livingstone; 2009:chap 189.

Raoult D. Rickettsial infections, In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 335.

Update Date 5/19/2013

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