Sample Collection For Skin Disease Investigation

The aim of carrying out laboratory investigations is to achieve a definite diagnosis and/or rule out conditions from the differential list suggested by the initial work-up. Correctly taken samples submitted in the appropriate manner to the laboratory will improve reliability of results.

Skin Scraping

This should sample the surface, epidermis and the upper dermis. Areas of crusting should be avoided. The hair is clipped and a scalpel blade dragged repeatedly over the skin. The sample can be submitted in a sterile container (blade may be included). Scraping should continue until capillary oozing occurs.

Plucked Hairs

Plucked hairs should be submitted (if checked with Wood's light and there are fluorescing hairs; these can be selected) for microscopic examination for dermatophytes and dermatophyte culture.

Impression Smear

For examination for Malassezia, a clean glass slide can be used to make an impression smear of the surface, which can be submitted unstained and air-dried to the laboratory.

Swab for Bacteriology

A swab in transport media is required for this examination. Using a sterile needle, pustules are opened and pus collected. If discharging fistulae are being sampled, the surface should be cleaned first with alcohol and allowed to dry before squeezing out discharge material, which can be collected uncontaminated on to the swab.

Punch biopsy specimens can also be submitted for culture. If a biopsy is submitted, a swab in transport media should also be included.

If patient is undergoing antibiotic therapy, withdrawal of treatment for five to seven days prior to sampling would be advised.

Correctly taken samples should allow meaningful examination for ectoparasites, dermatophytes, Malassezia and bacterial pathogens.