Fungal Infections

Laboratory testing

A precise mycological diagnosis is only possible with laboratory testing. In previous years, only a positive culture could truly define a fungal infection. With improved diagnostics now available, confirmation of the cause of a fungal infection is possible with serological and molecular (PCR) testing. However, getting good answers from the laboratory depends on a number of key factors which include:

  • Getting a high quality sample. Some nail and respiratory samples, for example, are not large enough, or saliva is submitted instead of sputum, see videos on how to collect excellent skin, hair and nails samples.
  • Testing before antifungal therapy is given. Some tests are more likely to be negative if antifungals have been given
  • Blood cultures in patients with Candida bloodstream infections are more likely to be positive if at least 20mL of blood is cultured. 
  • Sample processing in the laboratory. Cultures are more often positive when specific fungal media (usually Sabouraud dextrose agar) is used. Processing of the sample is important and not well studied. Temperature of cultures is a major factor in yield.
  • False positive Aspergillus antigen tests are possible with some antibiotics and foods, and occasionally in Histoplasma infections.

The tests that should be done on different samples, depends on the disease being considered. 

A guide on to how to process different samples can be viewed here.

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