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KOH prep
Fungal smear
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Potassium hydroxide preparation; Fungal culture; Fungal antigen and antibody tests; Calcofluor white stain
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Este artigo foi modificado pela última vez em 10 de Julho de 2017.
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Common Questions
  • How is it used?

    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 bases his choice(s) on practice guidelines and his 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 acute and convalescent antibody tests are ordered to see if antibody levels (titers) are changing, the evaluation of results may take several weeks.

  • When is it ordered?

    Fungal tests are ordered whenever a doctor suspects that a patient may have a fungal infection. They may also be ordered after or periodically during treatment to evaluate its effectiveness. In some patients, fungal tests may be ordered 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 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, rapid heartbeat
    • Central nervous system (CNS) infections (meningitis) may cause severe persistent headache, stiff neck, and sensitivity to light.
  • What does the test result mean?

    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:

    Tests for Superficial Fungal Infections

    Test Name
    Sample Type(s) Description UsesTime for Results
    KOH prep (potassium hydroxide solution)

    Skin scrapings, hair or nail clippings, tissue, vaginal swab, body fluids, sputum
    Board certification recommended
    Dissolves non-fungal elements in a sample. Reveals yeast cells and fungal hyphae (branching filaments) on a microscope slide. Primary screening tool. Detects fungi but does not tell what specific fungus is present Rapid
    Calcofluor white stain
    Skin scrapings, hair or nail clippings, vaginal swab, body fluids, sputum Stain binds to fungal elements in a sample and fluoresces under ultraviolet light. Allows visualization on microscope slide. More sensitive means of visualizing fungi. Detects fungi but does not tell what specific fungus is present. Rapid
    Fungal Culture
    Skin, nail, hair, body fluids, tissue, vaginal swab, sputum, blood A sample is inoculated onto or into nutrient media and incubated to grow any fungi present in sample. Primary tool to diagnose a fungal infection. Grows fungi for identification tests and subsequent susceptibility testing. Weeks

    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:

    Tests for Systemic Fungal Infections

    Test Name
    Sample Type(s) Description UsesTime for Results
    Susceptibility testing
    Sample of fungus isolated in culture Follow-up to fungal culture. When a pathogenic fungus has been identified, susceptibility is sometimes ordered to determine the most effective antifungal agent(s) to use. Guide treatment Days to weeks after culture
    Antigen testing
    Blood, CSF, body fluids Detects proteins associated with a specific fungus. This type of test available for a variety of fungi. Diagnose infection by specific fungus Day(s)
    Antibody testing
    Blood, CSF, body fluids Detects immune response to a specific fungus. May be ordered as a single sample or as acute and convalescent samples collected 2 to 3 weeks apart. Diagnose current or recent infection by specific fungus; monitor treatment Day(s) or Weeks
    Molecular tests for DNA, RNA Sample of fungus isolated in culture, blood, CSF, body fluids Detects genetic material of a specific fungus. Detects some fungi; not yet widely available, some in research settings only Days to weeks

    If fungal elements are identified in a KOH prep or Calcofluor white stain, then a fungus is present in the sample and may be causing the symptoms a patient is experiencing or be present as a harmless colonizer of the skin. The presence of multiple organisms in a fungal culture may indicate multiple pathogens or a mixture of pathogens and normal flora. If there is only normal flora present in the culture, then the infection may be due to an opportunistic fungus (part of the normal flora), the pathogen may have been missed in the sample, or the condition may be due to another cause.

    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 levels of antibodies in two serum samples, measured as acute and convalescent tests, can indicate an active or recent fungal infection. Some infected patients with compromised immune systems may have lower than expected antibody levels.

    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.

  • Is there anything else I should know?
    Fungal infections must frequently 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 – Ordered when a mycobacterial infection such as tuberculosis is suspected.
    • Blood culture – Ordered when septicemia 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 minimized 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.

  • If I have a persistent cough and fever, why would my doctor ask me where I have been traveling and what activities I have been doing?
    Some fungi are found in distinct geographical regions, such in the southwestern U.S. or midwestern U.S. If you have been around excavation or spelunking in caves, 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 Traveler’s Diseases.)
  • If my doctor thinks I have a fungal infection, why is he testing me for tuberculosis? 
    Many of the signs and symptoms associated with fungal lung infections could also be due to a tuberculosis infection. Generally, a doctor would order tuberculosis testing (such as an AFB smear and culture) to rule out a mycobacterial infection as the cause of your symptoms. The organisms that cause both conditions tend to be slow-growing – both in the body and in the laboratory.
  • Why would my doctor take multiple kinds of samples? 
    Multiple samples may be taken to evaluate how far into the body an infection has spread and sometimes to increase the likelihood that the fungus will be recovered.
  • Will my fungal infection eventually resolve itself without treatment? 
    Some may, but most persist without treatment. Lung and systemic infections may grow progressively worse and cause permanent tissue and organ damage even when symptoms are not severe. Some deep infections are almost uniformly fatal without treatment.
  • Is it really necessary to continue treatment for a long period of time? 
    Yes. Even if you start feeling better in a short period of time, you should follow your doctor’s recommendations. While yeast infections may resolve within a few days to weeks, some fungal infections may require months or even years of consistent treatment.