Test Overview

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 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

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.

Risks

There are no known risks from having this test.

Results

Normal

No evidence of fungus is found in the sample.

Abnormal

Evidence of fungus is found.