KOH Preparation
Doctors use the KOH preparation test to find out if you have a fungal infection. This kind of infection can happen in various parts of the body, such as the skin, nails, mouth, or vagina.
KOH is the abbreviation for potassium hydroxide, the solution that is used in the test.
Why It Is Done
Your doctor may do a KOH test to find out if you have a fungal infection, such as ringworm, athlete's foot, or a fungal nail infection. A KOH test can help find out if fungus is causing the infection, but it can't tell which type of fungus it is.
How To Prepare
In general, there's nothing you have to do before this test, unless your doctor tells you to.
How It Is 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 It Feels
You may feel a scraping sensation when the doctor or nurse takes the sample. The scraping takes only a few seconds.
It may be uncomfortable if a sample is scraped from under a fingernail or toenail, or if the area is sore, such as when you have thrush.
Credits
Current as of: September 25, 2025
Author: Ignite Healthwise, LLC Staff
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All Ignite Healthwise, LLC education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.
