Fungal Tests

Fungal tests are used to help detect and diagnose a fungal infection, to help guide treatment, and/or sometimes to monitor the effectiveness of treatment. For many superficial skin and yeast infections, a clinical examination of the patient and microscopic examination of the sample may be sufficient to determine that a fungal infection is present. The specific organism is not always identified. The doctor has several topical and oral antifungal treatment options and will base their choice(s) on best practice guidelines and personal experience.

Fungal cultures are used to identify the specific fungi present in persistent fungal infections and in those that penetrate into deeper tissues, affect the lungs, or cause systemic infections. Many fungi are slow-growing. The nutrient media used to recover them typically inhibits bacterial growth and must support fungal growth for several weeks. Susceptibility testing performed on fungi isolated from a culture is used to determine which antifungal is best to use for treatment.

Blood tests for fungal antigens and antibodies may be used to determine if a patient has, or recently had, a specific fungal infection. They are more rapid than fungal cultures but only test for a specific fungal species, so the doctor has to know what fungal organism to test for. Many people have fungal antibodies from a prior exposure to the organism so that a single antibody test may not confirm the presence of a current infection. If antibody tests are requested to see if antibody concentrations (titres) are changing, the evaluation of results may take several weeks.

Fungal tests are requested whenever a doctor suspects that a patient may have a fungal infection. They may also be requested after or periodically during treatment to evaluate its effectiveness. In some patients, fungal tests may be requested periodically to monitor for infection recurrence. Many signs and symptoms of fungal infections are similar to those caused by bacteria and/or viruses, and fungal tests are often requested when it is not clear what is causing the condition.

For superficial infections, tests may be requested when symptoms involving skin, nails, or mucous membranes appear, for example:

• Itchy, red, scaly areas of skin
• Nails that are thickened, brittle, and/or deformed
• White patches in the mouth (thrush)
• Vaginal itching and discharge (yeast infection)

Deep and systemic fungal infections may cause a variety of symptoms depending on the part of the body that is affected. Some examples include:

• Lung infections may produce flu-like symptoms such as coughing, fever, muscle aches, headaches, and rashes.
• Blood infections (septicaemia) may cause chills, fever, nausea, rapid heartbeat
• Central nervous system (CNS) infections (meningitis) may cause severe persistent headache, stiff neck, and sensitivity to light.

Superficial Infections
Many superficial fungal infections are diagnosed based on a physical examination. In addition to general symptoms, many skin infections have characteristic signs (such as the appearance of infected nails) and typical locations on the body (such as athlete’s foot between the toes). A clinical evaluation cannot, however, definitively tell the doctor which microorganism is causing a fungal infection. A few laboratory tests may be useful in detecting and confirming a fungal infection and may help guide treatment. These may include:

Deep and Systemic Infections
When a more definitive diagnosis is needed, as in cases of persistent, deep, or systemic infections, more extensive testing may be required to identify which fungus is causing the infection and how it may best be treated. This usually involves a combination of the tests mentioned above plus the following tests:

If an antigen test is positive, then it is likely that the fungus identified is the cause of the person’s infection. A positive antibody test result in a single serum sample may indicate exposure to a specific fungus, but it does not indicate when the exposure occurred. Rising concentrations of antibodies in two serum samples, measured on the initial sample, and a follow up sample, can indicate an active or recent fungal infection. Some infected patients with compromised immune systems may have lower than expected antibody concentrations.

If there are no fungi recovered in the sample, then the patient may not have a fungal infection or the pathogen was not successfully recovered with the sample and test. 

Fungal infections may often need to be distinguished from infections due to other microorganisms, such as bacteria. In some cases, an infection may have both bacteria and fungi present. Tests that may be used to identify or rule out other causes include:

• Gram stain – A rapid test performed to microscopically detect bacteria and/or fungi in a sample.
• Bacterial culture – Used to rule out a bacterial infection or determine if concurrent bacterial infection exists.
• AFB smear and culture – Requested when a mycobacterial infection such as tuberculosis is suspected.
• Blood culture – Requested when septicaemia is suspected.

Fungi thrive in moist environments, such as public swimming pool and gym lockers, inside sweaty shoes, constrictive clothing, and in skin folds. Fungal skin infections can be minimised by wearing flip-flops or sandals to limit direct exposure, by changing socks frequently, drying out shoes, and keeping moist areas of the body clean and dry. 

Some fungi are found in distinct geographical regions, you may have been exposed to fungal spores. This can be true, even if travel was not recent. Lung infections caused by some fungi may emerge months to even years after exposure. (For more on this, see Traveller’s Diseases.)