Histoplasma complement fixation is a blood test that checks for infection from a fungus called Histoplasma capsulatum (H capsulatum), which causes the disease histoplasmosis.
How the Test is Performed
The sample is sent to a laboratory. There it is examined for histoplasma antibodies using a laboratory method called complement fixation. This technique checks if your body has produced substances called antibodies to a specific foreign substance (antigen), in this case H capsulatum.
Antibodies are specialized proteins that defend your 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 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.
How to Prepare for the Test
There is no special preparation for the test.
The absence of antibodies (negative test) is normal.
Veins and arteries vary in size from one person 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 lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
What Abnormal Results Mean
Abnormal results may mean you have an active histoplasmosis 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.
People who have been exposed to H capsulatum in the past may have antibodies to it, often at low levels. But they may not have shown signs of illness.
Why the Test is Performed
The test is done to detect histoplasmosis infection.
Chernecky CC, Berger BJ. Histoplasmosis serology - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:645-646.
Deepe GS Jr. Histoplasma capsulatum. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Updated Edition. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 265.