The complement fixation test to Coxiella burnetii (C burnetti) is a blood test that checks for infection due to bacterium called C burnetii, which causes Q fever.
How the Test is Performed
The sample is sent to a laboratory. There, a method called complement fixation is used to check if the body has produced substances called antibodies to a specific foreign substance (antigen), in this case C 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
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or bruising. This soon goes away.
Why the Test is Performed
This test is done to detect Q fever.
Absence of antibodies to C burnetii is normal. It means you do not have Q fever now or in the past.
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.
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.
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)
Ashihara Y, Kasahara Y, Nakamura RM. Immunoassays and immunochemistry. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 44.
Marrie TJ, Raoult D. Coxiella burnetti (Q fever). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 190.
Update Date 5/1/2015
Updated by: 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, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.