Fungal Nail Infections - Exams and Tests
To determine the cause of a nail
problem and diagnose a
fungal nail infection, your doctor:
- 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
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
fungal culture, which can determine which type of
fungus is present. Fungi typically grow slowly, so it can take several weeks
for a culture to produce test results.
Almost all fungal toenail infections are caused by a type
of fungus called a dermatophyte. Because of this, if
the KOH test shows there is a fungus present, your doctor may assume that the
fungal infection is caused by a dermatophyte and prescribe treatment. But
because one medicine may be more effective than another medicine against
certain types of fungus, your doctor may want to do a fungal culture.
Many insurance companies now require testing to verify a fungal infection
before they'll pay for medicines, which can be expensive.
Test that is rarely done
If the KOH preparation and fungal culture do not show the
presence of fungi but a fungal infection is still suspected, your doctor may
remove a small piece of nail and look at it under a microscope (nail