Koh Preparation

Fungal scraping or potassium hydroxide examination.

To diagnose scaly or pustular conditions of the skin, hair, and nails suspected of being caused by fungi.

Heat and potassium hydroxide (KOH) are used on a tissue sample to dissolve keratin (a hard protein substance) and keratinocytes, the keratin-making cells of the epidermis. This makes it possible to detect the microscopic presence of a fungus that would otherwise be obscured by these substances.

None.

• If the infection affects the scalp, the doctor plucks diseased or broken hairs. The scalp may also be scraped with a scalpel.
• In nail infections, the inner surface of the nail below the tip is scraped, or the part of the nail tip that appears abnormal is clipped off.
• In skin infections, the outer layer of the abnormal skin is scraped.

You are free to resume normal activities.

• The sample may be too small or taken from an area where there is no fungus.
• Previous treatment with antifungal medications may produce false-negative results.

If the abnormality is caused by a fungus, the infectious organism may be identified under the microscope. If no fungus can be seen, the test is considered negative. However, a single negative sample cannot rule out fungal infection because the organism may have been missed.

• It's noninvasive.
• It provides results faster than skin fungus culture.

False-negative results are more common than with skin fungus culture and may occur in about one-quarter of cases.

• If the test is positive, appropriate antifungal medication can be prescribed. Sometimes a fungal culture is ordered to confirm the result or further classify the fungus.
• If the test is negative, a second sample may be taken or a fungal culture may be done.