SKIN PREP (KOH) FOR FUNGUS OR SCABIES

Effective Date: 
Wed, 08/07/2013
Reviewed: 
Tue, 01/10/2017
Revised: 
Wed, 08/07/2013
Policy: 

Purpose and Scope:

Identification of fungal elements is better achieved by the addition of potassium
hydroxide solution (KOH). This strong base can dissolve tissue cells and
keratinized material, making fungal elements and other parasites such as
Sarcoptes scabei more visible; the high concentration of cellular chitin, makes
fungal elements resistant to the denaturation effects of KOH. Dimethyl
Sulfoxide (DMSO), an additive present in the KOH solution accelerates the
process in the absence of heat.

Procedure: 

Procedure
Specimen collection
Skin

1. Cleanse skin to be sampled with 70% alcohol to remove contaminating
microorganisms.
2. If a characteristic dermatophyte “ring” is present on the skin, collect
samples from the outer margin of the ring at its junction with the normal
skin. Otherwise, collect samples from areas where the skin appears to be
scaling.
3. Use the edge of a glass slide or scalpel to scrape off the surface skin scales.
4. Cover the specimen between two glass slides or place the scales in a folded
piece of paper, or other suitable container.
5. Label the specimen with the patient’s name and unit history number or
other identifying number.

Nail

1. Clean the nail with 70% alcohol to remove contaminating microorganisms.
2. Scrape away the top layers of the nail and collect the subsurface material.
3. Also remove a portion of debris from under the nail with a scalpel.
4. Place the collected material into a sterile specimen container.

Lab Procedure

Skin and Nail

1. Skin and nail samples should be thoroughly minced with a scalpel. The DMSO and KOH penetrate slowly or not at all into the interior of inadequately minced pieces.

2. Nail clippings can be progressively shaved with a scalpel and pulverized with mortar and pestle. Place the material to be examined onto a clean glass microscope slide.

3. Add 1-2 drops of 20% KOH with DMSO (Soluphyte) to the material.

4. Place a cover slip over the preparation.

5. Observe the prep by brightfield microscopy. The illumination on a brightfield microscope should be carefully adjusted. Hyaline fungi will be difficult to see if the illumination is improperly adjusted.

6. Fungi has definite cell walls.

7. Scabies has characteristic morphology (consult Baily & Scott’s)

Key Points: 

Reagents and Supplies:
• 20% KOH with DMSO (Soluphyte Hardy Diagnostics)
• 0.9% Sterile sodium chloride

Reagent Storage:

KOH shelf life is three years. Store at room temperature.

 REFERENCES

Baron, EJ, Finegold, SM: Baily & Scott’s Diagnostic Microbiology, 8th
Edition, St. Lousi, C.V. Mosby Company, 1990.

Kern, M: Medical Mycology, Philadelphia, F.A. Davis Company, 1990

Koneman, EW, Roberts, GD: Practical Laboratory Mycology, Baltimore,
the Williams and Wilkins Co., 1985.

Larone, DH: Medically Important Fungi, A Guide to Identification, 2nd
Edition, New York, Elsevier Science Publishing Co., 1987.

McGinnis, MR: Laboratory Handbook of Medical Mycology, New York
Press, 1980