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Subject: Fungal Wet Mount (KOH, Calcofluor)
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A direct examination for fungal elements may provide a rapid detection of fungal infection and is recommended for most types of specimens submitted for fungal culture.
This test is used for the direct detection of fungal forms in patient specimens. The specimen is processed to form a liquid suspension of the patient sample.
Solid specimens, such as tissues, should be minced to facilitate suspension.
The specimen may be suspended in saline or a 10% KOH solution. KOH may improve liquefaction of the specimen and also lyses host cells and keratin; fungal cells are resistant to KOH digestion.
A cover slip is added for examination with regular or phase-contrast light microscopy.
Calcofluor white, a fluorogenic dye that binds to specific polysaccharide bonds found in fungal cell walls, may be added to the KOH solution to improve microscopic visualization of fungi.
Turnaround time: 24 hours.
Specimens should be collected and transported according to guidelines for fungal culture of the specimen type.
Expected result: Negative.
Positive: Provides evidence of fungal infection. Fungal elements may be characterized on the basis of morphology (e.g., budding yeast, aseptate hyphae, conidia-forming structures consistent with Aspergillus species).
Negative: Fungal infection is not ruled out by a negative wet mount examination.
The morphology of objects must be examined carefully to exclude artifacts or nonspecific absorption of calcofluor dye to nonfungal objects, such as capillaries.