Various laboratory tests may be used to help diagnose and guide treatment of fungal infections. For detailed information, see the article on Fungal Tests.
Tests for superficial infections
Many fungal skin infections are diagnosed by a healthcare practitioner based on a clinical evaluation and experience. In addition to general symptoms, many skin infections have characteristic signs, such as the appearance of infected nails, or typical locations on the body, such as the growth of athlete's foot between the toes. A clinical evaluation cannot, however, definitively tell the healthcare practitioner which microbe is causing a fungal infection. A few laboratory tests may be useful in detecting and confirming a fungal infection and may help guide treatment. They may include:
- Microscopic examinations, such as potassium hydroxide (KOH) preparation and calcofluor white stain
- Fungal culture and susceptibility testing
Tests for deep tissue, lung, and systemic infections
Symptoms of lung and systemic fungal infections are frequently nonspecific and may be confused with those due to other microbes or another disease process. Laboratory testing is primarily used to diagnose these serious fungal infections, to identify the microbe responsible, and to determine its likely susceptibility to specific antimicrobial agents. Sometimes testing is also performed to detect and identify bacteria that may be causing a concurrent infection. The sample collected depends upon the suspected location(s) of the infection. It may include the collection of blood, sputum, urine, cerebrospinal fluid (CSF), and/or the collection of a tissue biopsy. Testing may include:
- Microscopic examination of the sample using techniques such as KOH prep and calcofluor white stain to determine whether or not the infection is due to a fungus.
- Fungal culture – this is the primary test used to diagnose a fungal infection. Many fungi are slow-growing and may require up to several weeks for detection and identification.
- Susceptibility testing – a follow-up test to the fungal culture that is sometimes ordered to help guide treatment.
- Antigen and Antibody testing – available for a variety of different fungi but only for deep or systemic infections; may be performed on blood or other body fluids, such as CSF. Antibody testing typically involves measuring the level or titer of antibody.
- Molecular testing may be used to detect the genetic material of the fungus causing the infection and may be performed on blood or other body fluids, or on a sample of the microbe grown in culture.
Other tests that may be ordered in conjunction with fungal tests include:
- Gram stain – a rapid test performed to microscopically detect bacteria and yeasts in a sample
- Bacterial culture – used to rule out bacterial infection or determine if a concurrent bacterial infection exists
- AFB testing – may be used to rule out tuberculosis or infection due to non-tuberculous mycobacteria
- Blood culture – ordered when a blood infection (septicemia) is suspected
- CSF analysis – to detect infection of the central nervous system
In some cases, imaging scans such as x-rays may be ordered to detect fungal masses, such as those that may develop in the sinuses or lungs, and to evaluate the extent of tissue damage.