What Is the Histoplasmosis Complement Test?
Histoplasmosis is an infection caused by the fungus Histoplasma capsulatum (H. capsulatum). The fungus is commonly found in the eastern United States, particularly in the Ohio and Mississippi river valleys. It is spread through bird and bat droppings that form mold in the soil.
Spores from the mold can become airborne and enter your lungs. Histoplasmosis typically impacts the lungs, but in advanced stages it can affect other parts of the body as well.
A histoplasma complement fixation test, also known as a histoplasma antibody test, is used to detect the presence of H. capsulatum antibodies in a patient’s bloodstream.
When the fungus enters the bloodstream, the body produces antibodies to fight the infection. The antibodies are the proteins that attach themselves to the fungus.
When Is the Test Ordered?
If you display symptoms of histoplasmosis and have recently traveled to a region of the United States where H. capsulatum is found, your doctor will likely order this test. Histoplasmosis can be difficult to diagnose because the symptoms are similar to those of a cold or the flu. They may include:
- fever and chills
- dry cough
- chest pain when breathing
This test may also be ordered to confirm the findings from an abnormal chest X-ray. Patients who have had histoplasmosis in the past may experience scarring of the lungs. When lung scarring is discovered on a patient’s chest X-ray, the physician may order a histoplasma complement fixation test to determine if histoplasmosis caused the scarring.
How Is the Test Administered?
The histoplasma complement fixation test is administered by a nurse or technician in a doctor’s office or clinical lab. You will be required to provide a blood sample, which is usually taken from a vein in your forearm with a small needle. The blood will be collected in a tube and sent to a lab for analysis.
No special preparation is necessary for this test.
What Are the Risks of the Test?
Patients undergoing a histoplasma complement fixation test may feel some discomfort when their blood is drawn. After the test, patients may experience pain or throbbing at the injection site.
In general, the risks of a histoplasma complement fixation test are minimal. Potential risks of any blood test include:
- difficulty obtaining a sample, resulting in multiple needle sticks
- excessive bleeding at the puncture site
- fainting or lightheadedness
- accumulation of blood under the skin (hematoma)
- infection at the puncture site
Interpreting Your Results
A negative result means that no H. capsulatum antibodies were present in your blood. This means that you do not have an active or previous infection.
If the test results are positive, this indicates the presence of a histoplasmosis infection. However, if your antibody levels are low, you may not have any symptoms.
Patients who experience symptoms but have negative test results may need to have their test repeated. Antibody levels typically increase as the disease progresses. In patients with an early-stage infection, antibody levels may be too low to detect using the histoplasma complement fixation test.
If symptoms persist, your physician may order additional histoplasma complement fixation tests. Values from these tests can be compared to determine if you have an active infection. An increase in antibody levels will indicate the presence of an infection.