If the specimen is skin, hair or nail, the background cellular material may mask fungal elements. Potassium hydroxide will dissolve the keratin in these specimens, thus making any fungi more visible.
If there are a lot of cellular material in sputum or vaginal secretions, KOH mount may be prepared to dissolve the background thus making any yeast more visible.
However a saline mount must be additionally done to quantitate epithelial cells and WBCs and note presence of Trichomonas.
How to prepare 10% KOH
Potassium hydroxide……….…………10 g
Glycerol…………………………….20 mls
Distilled water………………………80 mls
Dissolve KOH in water, and then add glycerol. Glycerol prevents crystallization of the reagent and allows KOH preparations to be maintained for two days before drying up.
The procedure of using 10% KOH
1. Place specimen on clean grease free slide.
2. Add a drop of 10% KOH.
3. Apply coverslip and gently warm the slide over a flame.
4. Gently press the coverslip to spread the already softened tissue evenly on the slide.
5. Examine under a microscope X10 then X40.
6. Record the findings
Potassium hydroxide is a highly corrosive deliquescent chemical, therefore handle it with great care and make sure the stock bottle of chemical is tightly stoppered after use’.
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