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Histoplasma complement fixation

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

A blood sample is needed.

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 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

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

The test is done to detect histoplasmosis infection.

Normal Results

The absence of antibodies (negative test) is normal.

What Abnormal Results Mean

Abnormal results (1:32 or higher) 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.

Risks

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)

Alternative Names

Histoplasma antibody test

Images

References

Deepe GS Jr. Histoplasma capsulatum. 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 265.

Iwen PC. Mycotic diseases. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 61.

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, Bethanne Black, and the A.D.A.M. Editorial Team.

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