Skin lesion KOH exam

Definition

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

How the test is performed

The lesion is scraped, using a blunt edge such as the edge of a microscope slide. The scrapings from the skin lesion are placed in a solution of potassium hydroxide (KOH) and examined under the microscope. The fungus can be seen, if present. This test is different from a saline (salt water) examination, since the KOH destroys all non-fungal cells, making it much easier to see the fungal material.

How to prepare for the test

There is no special preparation for the test.

How the test will feel

You may feel a pressure sensation when the lesion is scraped from the skin.

Why the test is performed

The test is performed when fungal infections of the skin are suspected.

Normal Values

The lack of fungus is normal and expected.

What abnormal results mean

The KOH smear shows hyphae or fungal organisms. This may indicate ringworm, athlete's foot, jock itch, or many other fungal infections.

What the risks are

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

Illustrations

Viral lesion culture

Page Content:

Potassium hydroxide examination of skin lesion; Fungal wet prep