KOH (potassium hydroxide) preparation for oral candidiasis (thrush)

Exam Overview

The KOH preparation test is used to determine whether oral candidiasis (thrush) is present in a person's mouth. A sample of skin is taken from the person's mouth by lightly scraping the white patches.

The sample is then placed on a slide with potassium hydroxide (KOH) solution and gently heated. This solution slowly dissolves the skin cells but not the yeast cells. The yeast cells can then be seen with a microscope. Color stains may be used so that the yeast cells are easier to see.

Why It Is Done

A KOH test may be done if a person has white patches in the mouth or on the tongue to determine whether the person has thrush.

Results

Findings of a KOH test may include the following.

Normal

No yeast or other fungi are present in the sample from the person's mouth.

Abnormal

Yeast or other fungi are present in the sample from the person's mouth.

What To Think About

Generally, a KOH test is not mandatory to diagnose thrush. Thrush can usually be detected on visual examination of the white patches in a person's mouth. However, a KOH test may be done if thrush does not respond to prescribed medications to determine whether drug-resistant strains of thrush are present.

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Author:	Amy Fackler, MA Merrill Hayden	Last Updated March 30, 2006
Medical Review:	Kathleen Romito, MD - Family Medicine Michael J. Sexton, MD - Pediatrics Emmett Francoeur, MDCM, CSPQ, FRCPC - Pediatrics
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