The skin lesion KOH exam is a test to diagnose a fungal infection of the skin.
How the Test is Performed
The health care provider scrapes the problem area of your skin, using a blunt edge, such as the edge of a microscope slide. The scrapings from the skin are placed in liquid containing the chemical potassium hydroxide (KOH). The liquid is examined under the microscope. KOH destroys all non-fungal cells. This 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 or pain when the provider scrapes your skin.
Why the Test is Performed
This test is done to diagnose a fungal infection of the skin.
No fungus is present.
There is a small risk of bleeding or infection from scraping the skin.
Potassium hydroxide examination of skin lesion
Elewski BE, Hughey LC, Sobera JO, Hay R. Fungal diseases. In: Bolognia JL, Jorizzo JL, Schaffer JV, eds. Dermatology. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 77.
Update Date 4/14/2015
Updated by: Kevin Berman, MD, PhD, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.