KOH Reagent: Uses, Composition, Preparation and Its Modifications

potassium hydroxide

Uses of KOH Reagent

KOH is the chemical formula of potassium hydroxide and KOH reagent uses for the rapid detection of fungal elements in a clinical specimen because it clears the specimen making fungal elements more visible during direct microscopic examination. It is very useful for the presumptive diagnosis of the type fungal infections in the field of diagnosis of fungal infections.

Composition of KOH Reagent

20% w/v solution

Potassium hydroxide pellets: 20 g

Distilled water (D/W):  up to 100 ml

Procedure of 20% KOH reagent Preparation

  1. Weigh 20 g potassium hydroxide pellets.
  2. Transfer the weighed pellets to a screw-cap bottle.
  3. Add 50 ml distilled water, and mix until the pellets dissolve completely.
  4. Pour remaining distilled water and make the volume up to  100 ml.
  5. Now, label the bottle and mark it as corrosive.
  6. Store the prepared reagent at room temperature.
  7. For clarification watch this clip.

Expiry date: The reagent is stable for up to 2 years.


Precaution is mandatory during handling potassium hydroxide pellets. It is a highly corrosive deliquescent chemical, thus handle it with great care and make sure the stock bottle of chemical is tightly stoppered after use.

Modifications of KOH Reagent

KOH Reagent with DMSO

Dimethyl sulphoxide (DMSO) is an organic solvent. This makes it easier to use KOH reagent from cumbersome steps like heating or waiting for a longer duration to clear the specimen making fungal elements more visible during direct microscopic examination. Therefore the addition of dimethylsulphoxide (DMSO) to the KOH reagent enables specimens to be examined immediately or after only a few minutes.

KOH  Reagent with Blue-Black Fountain Pen Ink

The ink does not stain fungi but it stains cells and other components in the skin. This modification is useful when Malassezia furfur is suspected.


  1. District Laboratory Manual in Tropical Countries, Part 2; Cambridge University Press
  2. Bailey & Scott’s Diagnostic Microbiology, Elsevier
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