Diagnosing onychomycosis.

The diagnosis of onychomycosis may require the use of mycological diagnostic testing to supplement the clinical presentation. In order to verify that onychomycosis is present, the viability, penetrance, and species of the fungal infection should be determined. The most common diagnostic tests are mycological culture, direct microscopic examination, histopathologic study, and polymerase chain reaction (PCR)-based tests. Each of these tests has individual strengths in satisfying the three criteria, with a minimum of two positive diagnostic tests being the gold standard for confirming all three diagnostic criteria.