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KOH (Potassium Hydroxide) Preparation

Exam Overview

Doctors use the KOH preparation to find out whether a fungal infection is present on the nails, skin, scalp, or beard.

A doctor or nurse takes a sample of skin by lightly scraping the infected area that is scaling or flaking.

The doctor or nurse places the nail, skin, or hair sample on a slide with potassium hydroxide (KOH) solution and gently heats it. This solution slowly dissolves the skin cells but not the fungus cells. The fungus cells are then visible with a microscope. Color stains may be used so that the fungus is easier to see.

Why It Is Done

A doctor may do a KOH test to find out whether a person has a fungal infection. Fungal infections may cause:

Results

Findings of a KOH test may include the following:

Normal

No fungi are present in the nail, skin, or hair samples.

Other tests may be done to find out the cause of the skin infection.

Abnormal

Fungi are present in the nail, skin, or hair samples.

What To Think About

Your doctor may be able to find out whether you have a fungal infection by the appearance of the rash and may not need to do a KOH test.

Complete the medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.

Credits

By Healthwise Staff
Kathleen Romito, MD - Family Medicine
John Pope, MD - Pediatrics
Last Revised December 21, 2012

Last Revised: December 21, 2012

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