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10% KOH Test for the detection of Fungal Elements in Skin, Nails & Hair

koh test - 10% KOH preparation - principle of KOH Test - Principle of KOH preparation - materials required for KOH test - procedure of KOH test

Hey, Good to see you here 😀 …… In this Article, we’re gonna discuss the KOH Preparation for the detection of Fungal elements in the specimen….. If you have any queries, don’t forget to mention in Comments…

10% Potassium hydroxide (KOH) preparation is one of the easiest method used for the rapid detection of fungal elements like hyphae from the various clinical specimens.

KOH mount makes it more clear to visualize the fungal elements during direct microscopic examination. but the sensitivity of this test is quite low (approx. 30-60%) and cannot be used as the confirmatory test.

The principle of 10% KOH Preparation

Potassium hydroxide (KOH) is a strong alkali (having pH 11) which facilitates the microscopic observation of fungal elements.

When the specimen like Skin, Nails, Hair, sputum or any body fluids mixed with the !0% KOH solution, digests, softens and dissolve out the tissues & debris surrounding the fungal cells and the hyphae & conidia (spores ) of fungi can be easily observed under the microscope.

How to Prepare 100 ml of 10% KOH solution for KOH Test

 Weigh 10-gram potassium hydroxide (KOH) pellets on a weighing scale.

 Carefully Transfer the weighed KOH pellets to a screw-cap bottle.

 Now Add 50 ml of distilled water and mix well until the KOH pellets completely dissolved.

 Finally, add the remaining amount of distilled water and make the volume 100 ml.

 Label the bottle containing 10% KOH solution and Mark it corrosive.

Note: Potassium hydroxide (KOH) is highly corrosive chemical, therefore handi it with care and make sure to mark bottle as Corrosive and tightly capped.

 Store it at room temperature. The reagent is stable for about 2 years from the date of preparation.

Materials Required for the 10% KOH Preparation for fungal detection

  • 10% Potassium hydroxide (KOH) Solution
  • Alcohol Swab
  • Glass slides
  • Coverslips
  • Scalpel or Curette
  • Specimen (Skin, Nails, Hair etc.)

The procedure of 10% KOH Preparation for the detection of Fungal Elements

For Skin Specimen

 Obtain the Skin specimen from the site of lesion, if there is characteristic visible lesion like dermatophyte ring then collect the specimen from the outer margin of the Dermatophyte ring.

 If there is no characteristics lesions appear then obtain the specimen from areas where the skin appears to be scaling.

 Use the edge of the sterilized glass slide or the scalpel to scrape off the surface skin scales.

Note: Do not use cotton swabs because the cotton fibers may resemble hyphae resulting in false positive results.

 Place the sample on a labeled glass slide and instill a drop of 10% KOH solution then apply a coverslip.

For Nails Specimen

 If it is possible to cut the nail then obtain the nail specimen using a straight or curved mayo and cut a small portion of the affected nail.

 If it is not possible to cut the nail then scrape the nail area using a curette or scalpel.

 Place the sample on a labeled glass slide and instill a drop of 10% KOH solution over the specimen then apply a coverslip on it.

For Hair Specimen

 Clip off the lower end of the hair using a sterile straight mayo or scissors & also scrape the nearby area of the lesion with the help of sterile curette or scalpel.

 Place the specimen onto a sterile glass slide and instill a drop of 10 % KOH over the specimen then apply a coverslip on it

Finally, Observe under the microscope initially with a low power objective lens (10x) with reduced light looking for fungal elements such as yeast cells and hyphae etc.

Afterward, Change to high power objectives (40x) in order to verify fungal elements seen with the low power 10x objective

Malassezia furfur yeast cells - koh preparation
Malassezia furfur yeast cells and hyphae in KOH blue–black ink preparation.
Image Source: Microbeonline

Limitations of the KOH Preparation

 Some Experience is required in order to get the best results of KOH preparation as the background artifacts are often confusing on KOH mounts.

 The Clearing of some specimens especially the nails may require extended time and many time gives false negative results if not properly cleared.

 The KOH preparation of the specimen should be done as soon as the specimen is obtained in order to get the true results.

 Sometimes the quantity of few elements like yeast cells is not enough which can easily be observed and often skipped during observation if you’re not much experienced. so in order to get true results one must focus & observe carefully under the microscope.

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