KOH (Potassium Hydroxide) Preparation
The KOH (potassium hydroxide) preparation is used to find out whether a fungal infection is present on the skin.
A sample of skin is taken by lightly scraping the infected area.
Treatment of Actinic Keratosis
Some citations in the text of this section are followed by a level of evidence. The PDQ editorial boards use a formal ranking system to help the reader judge the strength of evidence linked to the reported results of a therapeutic strategy. (Refer to the PDQ summary on Levels of Evidence for more information.) Actinic keratoses commonly appear in areas of chronic sun exposure, such as the face and dorsa of the hands. Actinic cheilitis is a related condition that usually appears on the lower lips...
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The skin sample is placed on a slide with KOH solution and the solvent DMSO. This solution slowly dissolves the skin cells but not the fungus cells. The fungus cells can then be seen with a microscope. Color stains may be used so that the fungus is easier to see.
Why It Is Done
If you have patches of skin that are itchy, red, or scaly with bumps that look like blisters on the edges, a KOH test may be done to find out whether you have a fungal infection of the skin.
Results
Findings of a KOH test may include the following:
Normal
No fungi are present in the skin samples.
Abnormal
Fungi are present in the skin samples.
What To Think About
A doctor may be able to know if you have a fungal infection by the appearance of the rash and may not need to do a KOH test.
If the KOH preparation shows that you do not have a fungal infection, other tests may be done to figure out the cause of the skin problem.
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