Laboratory tests for fungal infection

Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2003.

Introduction

To establish or confirm the diagnosis of a fungal infection, skin, hair and nail tissue is collected for microscopy and culture (mycology).

Exposing the site to long wavelength ultraviolet radiation (Wood lamp) can help identify some fungal infections of hair (tinea capitis) because the infected hair fluoresces green.

Specimen collection for fungal testing

Specimens for fungal microscopy and culture may be:

They are transported in a sterile container or a black paper envelope.

Direct microscopy of skin scrapings and nail clippings

The material is examined by microscopy by one or more of these methods:

Microscopy can identify a dermatophyte by the presence of:

Fungal elements are sometimes difficult to find, especially if the tissue is very inflamed, so a negative result does not rule out fungal infection.

A yeast infection can be identified by the presence of:

Culture of fungi

Culture identifies which organism is responsible for the infection:

Growing the fungus in culture may take several weeks, incubated at 25-30ºC. The specimen is inoculated into a medium such as Sabouraud's dextrose agar containing cycloheximide and chloramphenicol. The cycloheximide is left out if a mould requires identification.

A negative culture may arise because:

Culture of yeasts and moulds may be due to harmless colonisation rather than infection. The infection may be secondary to an underlying skin disesase such as psoriasis.

Blood tests for patients with deep or disseminated fungal infection

Blood tests are not useful for the diagnosis of superficial fungal infections. But in subcutaneous and systemic infection, several tests may be useful.

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