Fungus Identification 101

May 1, 2005

What is the best way to obtain skin scrapings and evaluate them for evidence of fungal infection?

What is the best way to obtain skin scrapings and evaluate them for evidence of fungal infection?

- MD

There are several methods by which material for potassium hydroxide examination for fungal elements can be collected. A very effective method is to stroke the affected skin gently with a glass slide to produce scale, which is collected on another glass slide. With some hyperkeratotic lesions, preparatory debriding of excess keratin is recommended to make the examination more efficient.

The edge of a scalpel can also be used; however, use of a scalpel increases the risk of accidentally cutting the patient. Some sites can be debrided with an alcohol wipe, especially when maceration or weeping is present, but remember that alcohol stings.

Once you have obtained the specimen, apply a thin layer of potassium hydroxide to the scrapings on the slide, then gently heat the undersurface of the slide with a match to melt the keratin and thus facilitate the identification of fungal elements. Do not heat the slide to the point at which the potassium hydroxide bubbles; if this happens, the chemical will crystallize and make identification more difficult.

It is not uncommon for even experienced clinicians to require more than one attempt to identify fungal elements. To build competence at identifying fungi, practice on patients in whom tinea versicolor is suspected (Figure). In this condition, fungal elements are abundant and can be identified quickly and relatively easily.

- David L. Kaplan, MD
   Clinical Assistant Professor of Dermatology
   University of Missouri Kansas City School of Medicine