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Tests and diagnosis
By Mayo Clinic staffHistoplasmosis can cause a variety of signs and symptoms, many of which resemble those of other illnesses. For that reason, it can be particularly challenging to diagnose. Complicating the matter further is the large number of tests available for detecting the presence of the fungus — each of which has some limitations. These tests include:
- Fungal culture. This is considered the gold standard for confirming a diagnosis of histoplasmosis. During the test, a small amount of blood, sputum or tissue from your lymph nodes, lung or bone marrow is placed on a medium that enhances the growth of fungus and then checked for the presence of H. capsulatum. The drawback is the time it takes for the fungus to grow — two to four weeks and sometimes up to 12 weeks. For that reason, it's not a good choice in cases of disseminated disease where delayed treatment may prove fatal.
- Fungal stain. In this test, a tissue sample, which may be taken from sutum, bone marrow, your lungs or a skin sore, is stained with dye and examined under a microscope. The accuracy of the test depends on the type of sample obtained and the skill and experience of the examiner. Other organisms can resemble H. capsulatum under the microscope, so confirmation with another test is desirable if an organism resembling H. capsulatum is identified.
- Serology. This test examines blood for antigens and antibodies. It's a quick and fairly accurate way of detecting disseminated histoplasmosis as well as chronic or mild cases of the disease. But false-negative results are a problem, especially in people who have compromised immune systems or are infected with other types of fungi. The test can also be positive in people who live in endemic areas and have had past exposure to H. capsulatum, even though their current symptoms may be due to something else.
Depending on your signs and symptoms and the severity of your illness, your doctor may recommend other tests, such as:
- Chest X-ray. Although not normally used to diagnose histoplasmosis, an ordinary chest X-ray can show inflammation and damage in your lungs.
- Computerized tomography (CT). This X-ray technique produces more detailed images than do standard X-rays. CT can be especially helpful for detecting complications from histoplasmosis.
- Bronchoscopy. Your doctor may use this test to help establish a diagnosis of histoplasmosis if the disease hasn't already been confirmed by a fungal culture, stain or serology test. During the procedure, your doctor examines your windpipe (trachea) and the air passages leading to your lungs using a thin, lighted tube (endoscope). A small sample of tissue (biopsy) can be taken through the endoscope.
