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
How the Test is Performed
The health care provider scrapes the problem area of your skin using a needle or scalpel blade. 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.
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.
What Abnormal Results Mean
If the results are uncertain, a skin biopsy may need to be done.
There is a small risk of bleeding or infection from scraping the skin.
Chernecky CC, Berger BJ. Potassium hydroxide preparation (KOH wet mount) - specimen. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:898-899.
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.
Reviewed 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, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.