Skip to Content
Home > Wellness > Health Library > KOH (Potassium Hydroxide) Preparation for Fungal Nail Infections
It is not always possible to accurately
fungal nail infection based on appearance alone. A
potassium hydroxide (KOH) preparation test can help determine whether you have
a fungal nail infection.
Your doctor will collect a sample of skin
and/or nail fragments (debris) under the infected nail. If a sample of debris
can't be removed, he or she can take a nail sample by lightly scraping the
nail near the infected area or by using a small blade to shave off a piece of
Nail or debris samples are placed on a slide with a
potassium hydroxide (KOH) solution and gently heated. The solution slowly
dissolves the skin and nail cells, leaving the fungus cells. The fungus cells
can then be seen with a microscope. Color stains can be used to make the fungi
easier to see.
If you have discolored, damaged,
broken, or thickened nails or have a buildup of skin and nail fragments
(debris) under a nail, a KOH test can help confirm whether a fungal nail
infection is present.
No fungi are present in the debris or nail
sample. But the test may be done again using more samples taken from other
parts of the infected nail. This is because there may no longer be fungi on the
edge of the infected area, where it is easiest to scrape for a sample, or in
the dead tissue, even if you have a fungal nail infection.
Fungi are present in the debris or nail
Not all nail diseases
are fungal nail infections. Because of this and the
risks linked with oral antifungal medicine, your
doctor will probably confirm that you have a fungal infection using a KOH
preparation test if you are considering taking antifungal pills (oral
treatment). Many insurance companies now require testing to verify a fungal
infection before paying for medicines.
If your test is normal, your doctor may
do other tests to determine the cause of the nail damage.
Complete the medical test information form (PDF)medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.
Current as of:
March 12, 2014
Patrice Burgess, MD - Family Medicine & E. Gregory Thompson, MD - Internal Medicine
How this information was developed to help you make better health decisions.
To learn more, visit Healthwise.org
© 1995-2014 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
Our interactive Decision Points guide you through making key health decisions by combining medical information with your personal information.
You'll find Decision Points to help you answer questions about:
Get started learning more about your health!
Our Interactive Tools can help you make smart decisions for a healthier life. You'll find personal calculators and tools for health and fitness, lifestyle checkups, and pregnancy.
Feeling under the weather?
Use our interactive symptom checker to evaluate your symptoms and determine appropriate action or treatment.