Histoplasma complement fixation is a blood test that checks for infection due to a fungus called Histoplasma capsulatum (H. capsulatum), which causes the disease histoplasmosis.
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 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 Histoplasma capsulatum. Antibodies 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 to Prepare for the Test
There is no special preparation for the test.
How the Test will Feel
You may feel a prick or stinging sensation when the needle is inserted to draw your blood. Some people may have moderate pain. Afterward, there may be some throbbing.
Why the Test is Performed
The test is done to detect histoplasmosis infection.
The absence of antibodies (negative test) is normal.
What Abnormal Results Mean
Abnormal results may mean you have an active histoplasmosis 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)
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.
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.
Histoplasma antibody test
Kauffman CA. Histoplasmosis. In: Goldman L, Schafer Al, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 340.
Deepe GS Jr. Histoplasma capsulatum. 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 264.
Update Date 5/19/2013
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. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial Team.