The KOH (potassium hydroxide) preparation is used to determine whether a fungal infection is present on the skin.

A sample of skin is taken by lightly scraping the infected area.

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

Why It Is Done

If you have patches of skin that are itchy, red, or scaly with blisterlike bumps on the edges, a KOH test may be done to determine whether you have a fungal infection of the skin.

Results

Findings of a KOH test may include the following:

Normal

No fungi are present in the skin samples.

Abnormal

Fungi are present in the skin samples.

What To Think About

A health professional may be able to determine whether it is a fungal infection by the appearance of the rash and may not need to do a KOH test.

If the KOH preparation shows that you do not have a fungal infection, other tests may be done to determine the cause of the skin problem.

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