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Skin lesion KOH exam

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

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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 when the health care provider scrapes your skin.

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

Normal Results
No fungus is present.

What Abnormal Results Mean
Fungus is present. The fungus 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 skin.

Alternative Names
Potassium hydroxide examination of skin lesion

References
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: 4/14/2013
Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.
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