Fungal Nail Infections - Exams and Tests

Exams and Tests

To determine the cause of a nail problem and diagnose a fungal nail infection, your health professional:

• Will ask about your medical history, including any previous symptoms of nail damage or fungal nail infections.
• Will look at the skin and nails on your hands and feet.
• May take a sample of the bits of skin and nail fragments (debris) from under the infected nail. If a sample of debris cannot be taken easily, a nail sample may be taken by lightly scraping the nail near the infected area or by using a small blade to shave off a piece of nail.

Tests used to examine nail and debris samples include:

• KOH (potassium hydroxide) preparation, to determine whether the nail or skin condition is caused by fungi. This test can be done in a clinic or doctor's office.
• A fungal culture, which can determine which type of fungus is present. Since fungi generally grow slowly, it can take several weeks for a culture to produce test results.

About 90% of fungal toenail infections are caused by a type of fungus called a dermatophyte.¹ Because of this, if the KOH test shows there is a fungus present, your health professional may assume that the fungal infection is caused by a dermatophyte and prescribe treatment. However, because one medication may be more effective against certain types of fungus than another medication, your health professional may want to do a fungal culture.

Many insurance companies now require testing to verify a fungal infection before they'll pay for medications, which can be expensive.

Tests that are rarely done If the KOH preparation and fungal culture do not show the presence of fungi but a fungal infection is still suspected, your health professional may remove a small piece of nail and look at it under a microscope (nail biopsy).