Skin lesion KOH examDefinition: The skin lesion KOH exam is a test to diagnose a fungal infection of the skin.
Alternative Names: Potassium hydroxide examination of skin lesion; Fungal wet prep
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.
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