The KOH preparation test is used to
find out whether oral candidiasis (thrush) is
present in a person's mouth. A sample of skin is taken from the person's mouth
by lightly scraping the white patches.
The sample is then placed
on a slide with potassium hydroxide (KOH) solution and gently heated. This
solution slowly dissolves the skin cells but not the yeast cells. The yeast
cells can then be seen with a microscope. Color stains may be used so that the
yeast cells are easier to see.