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Blood test

Histoplasma complement fixation

Definition

Histoplasma complement fixation is a blood test that checks for signs of infection due to a fungus called Histoplasma capsulatum (H. capsulatum). Some people who breathe in particles of this fungus may get an infection called histoplasmosis.

See also:

• Histoplasmosis - chronic pulmonary
• Histoplasmosis - disseminated
• Histoplasmosis - acute (primary) pulmonary
• Histoplasmosis - skin lesion

Alternative Names

Histoplasma antibody test

Why the Test is Performed

Histoplasma complement fixation is one of the most commonly used methods to test for a fungal infection caused by H. capsulatum.

How the Test is Performed

You will need to give a blood sample.

The complement fixation test checks the blood for antibodies to H. capsulatum. Antibodies defend the body against bacteria, viruses, fungus, or other foreign body (antigen). Certain cells tell the body to produce antibodies during an active infection. If the antibodies are present, they stick, or "fix" themselves, to the antigen. That is why the test is called "fixation."

The test specifically looks for the antibodies in the clear liquid portion of the blood (serum). This general term for this method is called serology.

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.

Risks

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)

Normal Results

The absence of antibodies (negative test) is normal.

What Abnormal Results Mean

Abnormal results may indicate an active histoplasmosis infection.

People who have been exposed to H. capsulatum in the past may also have antibodies to it, often at low levels. However, they may not have shown signs of illness.

Note: In the initial stage of an illness, few antibodies may be detected. Antibody production increases during the course of an infection. For this reason, such tests are often repeated several weeks after the first test is done..

Review Date: 6/5/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; 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, Medical Director, A.D.A.M., Inc.