Histoplasma complement fixation

• Illustrations
• Alternative names
• Definition
• How the test is performed
• How to prepare for the test
• How the test will feel

• Why the test is performed
• Normal Values
• What abnormal results mean
• What the risks are
• Special considerations
• References

Alternative names    Return to top

Definition    Return to top

Histoplasma complement fixation is one of the most commonly used methods to test for antibodies to the fungus histoplasma capsulatum (H. capsulatum). People who breath in the fungus particles may get an infection called histoplasmosis.

How the test is performed    Return to top

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.

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.

The complement fixation test looks to see if the body has produced antibodies to a specific antigen --  in this case H. capsulatum. The test specifically looks for the antibodies in the clear liquid portion of the blood, which called the serum. This general term for this method is called serology.

If antibodies are present, they stick, or "fix" themselves, to the antigen.

How to prepare for the test    Return to top

There is no special preparation for the test.

How the test will feel    Return to top

You may feel a prick or stinging sensation when the needle is inserted. Others may have moderate pain. Afterward, there may be some throbbing.

Why the test is performed    Return to top

The test is performed to detect a fungal infection caused by histoplasma.

Normal Values    Return to top

The presence of no antibodies is normal.

What abnormal results mean    Return to top

Abnormal results may indicate an active histoplasmosis infection.

CF antibody concentration is expressed as a titer, which measures the amount of the antibody against the amount of the antigen in the blood. For example, 1:4.

A higher titer usually means more extensive infection.

Tests are often repeated 2 to 4 weeks after the initial sample it taken, since antibody production increases during the course of infection.

People who have been exposed to H. capsulatum in the past may also have antibodies, often at low levels. However, they may not have shown signs of illness. A repeated test that shows an increase in the titer number would suggest an active rather than prior infection.

See also:

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

What the risks are    Return to top

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Special considerations    Return to top

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.

References    Return to top