Skin lesion KOH exam

Definition

The skin lesion KOH exam is a test to diagnose a fungal infection of the skin.

Alternative Names

Potassium hydroxide examination of skin lesion

How the Test is Performed

The health care provider scrapes the lesion off your skin, using a blunt edge such as the edge of a microscope slide. The scrapings from the skin lesion are placed in liquid containing potassium hydroxide (KOH) and examined under the microscope. KOH destroys all non-fungal cells, which makes it easier to see if there is any fungus present.

How to Prepare for the Test

There is no special preparation for the test.

How the Test Will Feel

You may feel pressure when the doctor scrapes the lesion off your skin.

Why the Test is Performed

This test is done to diagnose a fungal infection of the skin.

Normal Results

Normally, there is no fungus.

What Abnormal Results Mean

The KOH smear shows fungus, which may be related to ringworm, athlete's foot, jock itch, or another fungal infection.

Risks

There is a small risk of bleeding or infection from scraping the lesion.

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