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Basics ⬇

Potassium Hydroxide Test and Fungal Culture*

The potassium hydroxide (KOH) examination provides an immediate diagnosis of a superficial fungal infection, whereas the results of a fungal culture may take weeks. It is a simple, rapid method to detect fungal elements in skin, nails, and hair.

Other Information ⬆

Technique !!navigator!!

Collection of Specimen

  • Collection is optimal when no surface artifacts (e.g., topical medications) are present.

Skin

  • Gently scrape scale from the “active border” with a no. 15 scalpel blade (Fig. 35.1).

Nails

  • Trim the nail.

  • Use a no. 15 scalpel blade or a 1- to 2-mm curette (Fig. 35.2) under the nail surface to obtain fine scale (thick specimens do not allow for cover slip application).

Hair

  • Pluck broken hairs with forceps or use a toothbrush to obtain scale and hairs (Fig. 35.3).

Preparation

  • Use a KOH solution such as Swartz-Lamkins Fungal Stain or a KOH solution with dimethyl sulfoxide.

  • Gather a thin layer of scale, or scale plus hair on a slide and cover it with a coverslip.

  • With an eyedropper, place a single drop of a KOH solution at the edge of the coverslip and allow it to spread under the coverslip by capillary action (Fig. 35.4).

  • Heat the undersurface of the slide gently with a lighter or a match until bubbling begins. Wipe undersurface of slide to remove black residue of heating (KOH solution with dimethyl sulfoxide does not require heating).

Observation

  • Begin with a low-power scan to identify scale and possibly hyphae.

  • Become aware of artifacts that are easily confused with hyphae and spores, such as hairs, clothing fibers, keratinocyte cell borders, and air bubbles.

  • Use higher power (40×) to confirm the presence of hyphae or spores (Figs. 35.5 to 35.11).

*N.B. Clinical Laboratory Improvement Act guidelines may require the practitioner to use outside laboratory facilities for conducting KOH examinations and fungal cultures.

Fungal Culture !!navigator!!

Outline