KOH test
A potassium hydroxide (KOH) test is done to determine whether a fungus is causing a skin infection. Samples from an infected area are treated with KOH, which dissolves skin cells and leaves behind fungus cells (if any are present) that can been seen with a microscope.
The KOH test may be used to diagnose fungal infections, such as thrush, tinea versicolor, and ringworm.
Why is a KOH preparation done?
Your doctor may do a KOH test to find out if you have one of these fungal infections:
- Ringworm of the scalp, skin, or beard.
- Athlete's foot.
- Fungal nail infection.
- Oral candidiasis (thrush).
- Vaginal yeast infection.
How is a KOH preparation done?
A doctor or nurse takes a sample by lightly scraping the infected area. Sometimes the doctor will use a swab.
The sample is then placed on a slide with potassium hydroxide (KOH) solution and is gently heated. This solution slowly dissolves the skin cells but not the fungus. The fungus can then be seen with a microscope. Color stains may be used so that the fungus is easier to see.
How do you prepare for a KOH preparation?
In general, there’s nothing you have to do before this test, unless your doctor tells you to.
What do the results of KOH preparation mean?
Normal
No evidence of fungus is found in the sample.
Abnormal
Evidence of fungus is found.
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