Potassium hydroxide (KOH) mount is a very useful test for the laboratory diagnosis of fungal infection of tissues especially skin, hair and nails. KOH separates the fungal elements from intact cells as it digests the protein debris and dissolves cement substances that holds the keratinized cells together and makes it easy to visualize under the microscope.

Requirements:

  1. 10% KOH
  2. Coverslip
  3. Glass slide
  4. Needle
  5. Bunsen flame
  6. Specimen

Method

There are two types of method to perform KOH mount

  1. Slide KOH
  2. Tube KOH

Slide KOH Procedure 

  • Place the specimens like epidermal scales, nail, hair, skin scrapping or tissue on a clean glass slide.
  • Pour a drop of 10% KOH on the specimen and place a converslip over it.
  • Heat the slide gently over flame.
  • Leave the slide for 5-10 minutes.
  • Examine the slide under microscope.

Note: If the specimen is not dissolved properly, it may be kept for some more time in a petridish containing filter paper soaked with water at its base. Too much of heating should be avoided so that crystals of KOH are not formed. Heating can be substituted by using Dimethyl sulfoxide (DMSO). A mixture of 20% KOH solution and equal part of Parker ink can be used for staining fungal elements.

Tube KOH

It is mainly done for the biopsy specimens that take longer time for dissolution. The homogenized tissue material is dissolved in 10% KOH and examined after keeping for an overnight in an incubator at 37°C. This procedure can also be used for nail clippings and skin biopsies which dissolve with difficulty and the concentration of KOH may be increased.

Observation of KOH mount

Shining fungal elements can be observed under microscope. Different fungal elements like hyphae, pseudohyphae, yeast cells, spores, spherules and sclerotic bodies can be seen clearly in a KOH wet mount.

If none of the fungal structures is found in the entire smear, report is dispatched as NO FUNGAL ELEMENTS SEEN”.                                                                    

Preparation of KOH solution for KOH mount

Ingredients

Potassium hydroxide (KOH) –           10 gm

Glycerol –                                            10 ml

Distilled water –                                 80ml

Dissolve KOH in distilled water and add glycerol to it. Glycerol is added to prevent drying. Mix these ingredients properly and store the solution at room temperature. Concentration of KOH can be increased up to 40% depending upon the nature of the specimen.

DMSO can be added to 20% KOH solution as it helps as best cleansing agent of fungi. (DMSO-40 ml, KOH -20 gm, Distilled water -60ml)

 

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