Fungal Tests

How is it used?

Fungal tests are used to help detect and diagnose a fungal infection, to help guide treatment, and/or to monitor the effectiveness of treatment.

• For many superficial skin and yeast infections, a clinical examination of the affected body part(s) 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 healthcare practitioner has several topical and oral antifungal treatment options and bases the choice(s) on practice guidelines and experience.
• For persistent, deeper, or systemic infections, several tests may be used for diagnosis and monitoring.
  • Fungal cultures are used to identify the specific Fungi present. Many fungi are slow-growing, so it may take weeks for results. Susceptibility Testing performed on fungi isolated from a culture is used to determine which antifungal is best to use for treatment.
  • Tests for fungal antigens and antibodies may be used to determine if an individual 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 healthcare practitioner has to know what fungal organism to test for. Many people have fungal antibodies from a prior exposure to the organism, so a single antibody test may not confirm the presence of a current infection. Sometimes, blood samples are collected 2 to 3 weeks apart (acute and convalescent samples) and tested to see if antibody levels (titers) are changing; the evaluation of these results may take several weeks.
  • Molecular tests may be performed to identify fungi grown in culture and sometimes may be used to detect a specific fungus directly in the sample collected. 

The following tables summarize uses of various fungal tests:

Tests for Superficial Fungal 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 help determine the treatment that may be most effective. This usually involves a combination of the tests mentioned above plus the following tests:

Tests for Systemic Fungal Infections

When is it ordered?

Fungal tests are ordered whenever a healthcare practitioner suspects that a person's signs and symptoms are due to a fungal infection. Many signs and symptoms of fungal infections are similar to those caused by bacteria and/or viruses, and fungal tests are often ordered when it is not clear what is causing the condition.

For superficial infections, tests may be ordered 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 (septicemia) may cause chills, fever, nausea, and rapid heartbeat.
• Central nervous system (CNS) infections (meningitis) may cause severe persistent headache, stiff neck, and sensitivity to light.

Fungal tests may also be ordered after or periodically during treatment to evaluate its effectiveness or to monitor for infection recurrence.

What does the test result mean?

Interpretation of fungal tests and examinations of slides and cultures often require experience in the study of fungi. Results must be carefully considered, along with signs and symptoms as well as medical history, and sometimes travel history, of the person tested.

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 healthcare practitioner which microbe is causing a fungal infection. Sometimes a microscopic examination or culture of a sample may be useful in detecting and confirming a fungal infection and may help guide treatment.

Some examples of superficial infections include:

• yeast infections caused by Candida species
• Athlete's foot
• Jock itch
• Scalp or hair infection
• Finger or toenail infection
• Ringworm

Deep Tissue, Lung, Blood, and Systemic Infections

In cases of persistent, deep, or systemic infections, a definitive diagnosis is needed and more extensive testing may be required to identify which fungus is causing the infection and to guide treatment. This usually involves a combination of several tests that may be performed on samples of sputum or tissue retrieved from the lungs, blood, urine, or spinal fluid. Examples of some serious fungal infections that may be require extensive testing include:

• Aspergillosis
• Blastomycosis
• Coccidioidomycosis
• Cryptococcosis
• Histoplasmosis

For more on these, see the article on fungal infections.

In general, a negative test result means that there is no fungal infection present and symptoms are likely due to another cause. A negative test after a person has been treated for a fungal infection means that the therapy has been successful.

Positive results generally indicate that a fungus is present and sometimes identify the type causing an infection:

• Microscopic examinations (KOH prep or Calcofluor white stain): in general, if fungal elements are seen, then a fungus is the likely the cause of symptoms. These tests, however, do not identify the fungus.
• Culture: care must be taken when interpreting culture results. Interpretation often depends on the type of sample.
  • For non-sterile sites, such as the skin, a positive culture will typically identify the fungus or fungi present. The fungi identified may be the type that are disease-causing (pathogenic), the type that only cause disease in people with weakened immune systems (opportunistic), or those that are part of the normal flora. A mixture of these types may also be present.
  • Sterile samples, such as blood, CSF, or tissues that are properly collected will not be contaminated with normal flora. A positive culture identifies the fungus or fungi causing the infection.
• A positive antigen test means that it is likely that the fungus tested is the cause of the person's infection.
• A positive antibody test result in a single blood sample indicates exposure to a specific fungus, but it does not indicate whether the exposure was recent or in the past. On the other hand, a rise in the level of antibody (titer) between two serum samples collected 2-3 weeks apart (acute and convalescent) indicates an active or recent fungal infection.
• Molecular tests: detection of a specific fungus with a molecular test indicates a likely infection with that fungus if the test was performed on a sample from a sterile body site, such as blood, CSF or tissue.

Is there anything else I should know?

If a fungus that is causing an infection is not present in sufficient amount in a sample, a test to detect and/or identify the fungus may be falsely negative.

For antibody testing, some infected individuals with weakened immune systems may not produce antibodies as expected.

fungal infections must frequently be distinguished from infections caused by other microbes, 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 Testing - ordered when a mycobacterial infection such as tuberculosis is suspected.
• Blood culture - ordered when septicemia is suspected.

Fungi thrive in moist environments, such as surfaces in and around public swimming pools and gym locker rooms, inside sweaty shoes and socks, in skin folds, and wherever skin is kept moist by constrictive clothing. Fungal skin infections can be minimized by wearing flip-flops or sandals when walking around the pool or locker room, by changing socks and underwear at least once a day, drying out shoes, and keeping moist areas of the body clean and dry.