What is a Histoplasma Skin Test?

    A histoplasma skin test is used to determine if you have been exposed to a fungus called Histoplasma capsulatum. This fungus can be found in bird droppings, bat droppings, and contaminated soil. Histoplasma capsulatum exposure can cause a medical condition called histoplasmosis.

    Histoplasmosis can present as a lung infection, a rash, or joint pain. The infection can affect almost any part of your body, including your eyes and nervous system. Other symptoms of histoplasmosis include:

    • achy muscles
    • headache
    • fever (with or without chills)
    • chest pain
    • dry cough

    Histoplasma skin tests are not ordered very often anymore. Blood and urine tests are more commonly used to confirm exposure to Histoplasma capsulatum.

    Reasons for a Histoplasma Skin Test 

    A histoplasma skin test may be ordered if blood or urine tests are inconclusive. A positive skin test does not mean that you have an active infection, although you could develop one in the future.

    Mild histoplasmosis may not cause you to experience any symptoms. However, infections can become serious and even life threatening. Severe histoplasmosis can lead to:

    • respiratory problems: lung damage and breathing difficulties
    • pericarditis: the inflammation of the sac surrounding your heart
    • adrenal insufficiency: damage to the adrenal glands that control hormone secretion in your body
    • meningitis: inflammation of the membranes surrounding your spinal cord and brain

    You might need a histoplasma skin test simply as precaution. People in certain occupations have an increased risk of exposure to Histoplasma capsulatum. Those who work with soil may be more likely to inhale the spores released by the fungus. Farmers, pest control specialists, landscape artists, and construction workers may be at risk for developing histoplasmosis. Professionals in these fields should consider having periodic histoplasma skin tests.

    Histoplasma Skin Test Procedure

    A histoplasma skin test is performed in your doctor’s office or an outpatient clinical laboratory. The test does not require special preparation and can be done at any time. The test takes just a few minutes to complete.

    A technician cleans your forearm with an antiseptic agent, such as an alcohol swab. Then, he or she injects a small amount of an allergen just under your skin. Allergens are substances that can provoke an allergic reaction, including animal dander, chemicals, and bacteria. Allergens are used in skin testing to determine if you have been exposed to a particular virus, bacteria, or fungus.

    After the allergen is injected, you can go home and continue with your daily routine, but you must return to the lab to have your skin checked. Follow-up appointments are usually scheduled for 24 to 48 hours after your skin test.

    Interpreting the Test Results

    The results of your histoplasma skin test are either “positive” or “negative.” A positive test means that you have tested positive for exposure to the fungus. The skin surrounding the injection site may become itchy, irritated, red, or inflamed if you have tested positive.

    Confirmed exposure to Histoplasma capsulatum may or may not require treatment. People who are asymptomatic do not need to take medications. Those who show symptoms of infection are treated with antifungal drugs.

    A negative test shows no skin changes and, therefore, no exposure to Histoplasma capsulatum.