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Fungal skin scraping
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A fungal skin scraping is the test used to look for a fungal infection of the skin. The doctor scrapes the affected area with a needle or the blade of a scalpel, places the scales on a slide, the glass plate used under the microscope, and adds a liquid containing potassium hydroxide, abbreviated KOH, on top of them.
That liquid has one job. It dissolves keratin, the tough protein of the skin, and much of the material inside the cells. With all of that gone, what is left visible is the fungus. KOH erases the skin from the slide and leaves only what is not skin.
In tinea, the skin infection caused by these fungi, what shows up under the microscope are hyphae: long, thin, branching filaments divided into segments by cross walls. It is worth knowing the limit: in up to 15% of cases the test comes back negative even though the fungus is there.
In brief
A fungal skin scraping lifts scales of skin with a needle or scalpel, places them on a slide, and adds potassium hydroxide.
Potassium hydroxide dissolves keratin and much of the cellular material, leaving the fungus visible under the microscope.
KOH erases the skin from the slide and leaves only what is not skin.
In tinea the hyphae appear septate, branching and narrow; even so, KOH is falsely negative in up to 15% of cases.
Sources (2)
- MedlinePlus, U.S. National Library of MedicineSkin lesion KOH exam, MedlinePlus Medical EncyclopediaPublished
- National Center for Biotechnology Information, StatPearls PublishingTinea Corporis, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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