KOH Preparation

Why It Is 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 To Prepare

You don't need to do anything before you have this test.

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.

What Affects the Test

Your doctor will talk with you about anything that might keep you from having the test or that may change the test results.

What To Think About

• It's possible to get a "normal" result when you have a fungal infection. This happens when the sample taken doesn't contain enough fungal cells to be seen in the test.
• If the test shows that you don't have a fungal infection, other tests may be done to figure out the cause of your symptoms.