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KOH with Calcofluor White

For the direct microscopic examination of skin scrapings, hairs, nails and other clinical specimens for fungal elements.

This is a very sensitive method, however, a fluorescence microscope with ultraviolet filters is required (Hageage and Harrington, 1984; Hollander et al. 1984; Monheit et al. 1984; Harrington and Hageage 2003).

Method

Solution A Potassium Hydroxide Reagent

  • Dissolve the KOH in water and add glycerol.
  • Potassium hydroxide 10 g
  • Glycerin 10 ml
  • Distilled water 80 mL

Solution B Calcofluor White Reagent

  • Dissolve Calcofluor white powder in the distilled water by gentle heating.
  • Calcofluor white 0.5 g
  • Evans blue 0.02 g
  • Distilled water 50 mL

Method for Making Microscopic Mounts

  1. Mix one drop of each solution on the centre of a clean microscope slide.
  2. Place the specimen in the solution and cover with a coverslip, squash the preparation with the butt of the inoculation needle and then blot off the excess fluid.
  3. Gently heat the slide and examine microscopically for the presence of fungal elements that fluoresce a chalk-white or brilliant apple green colour, depending on the filters used.

Comments: 
This is a very rapid and sensitive method, however a fluorescence microscope fitted with filters to give an excitation with ultraviolet light below 400 nm wavelength is required.

Further reading: 
Hageage and Harrington, Laboratory Medicine 1984,15:109-112

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