Skin lesion KOH exam
The skin lesion KOH exam is a test to diagnose a fungal infection of the skin.
Potassium hydroxide examination of skin lesion; Fungal wet prep
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.
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.
What the risks are
There is a small risk of bleeding or infection from scraping the lesion.
Jonathan Kantor, M.D., North Florida Dermatology Associates, Jacksonville, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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