Investigations

Swabs - for bacteriology, and virology if appropriate. In order to get a good sample it is important to dip the swab in the culture medium and then rub it against the skin

Skin scrapings or clippings for mycology. If taking specimens from nails it is important to take a good sized clipping and also scrape from the under surface of the nail otherwise a false negative result is much more likely. For tinea of the scalp take both skin scrapings and remove a few affected hairs as examination of the roots may be beneficial, or alternatively use a disposable plastic toothbrush (like those used by airlines). This latter technique involves brushing the affected area, place the lid back on the toothbrush and then send to microbiology. This can be highly effective but you will need to source a supplier and discuss with your local laboratories

Blood tests and imaging – see specific conditions listed under clinical guidelines. For immunological tests please refer to the section on immunology

Biopsy – can be used in the following ways:

• Histology (light microscopy) for pathological interpretation. Lesions sent for histology must be accompanied by relevant history, description and a differential diagnosis to aid the histopathologist in making the diagnosis. It must be remembered that histology is not the be all and end all of dermatology:
  • It does not always help when diagnosing difficult rashes - such patients are often instead best managed by being referred for a specialist opinion
  • It may fail to detect some cases of early lentigo maligna and cutaneous t-cell lymphoma
  • It can be difficult to differentiate histologically between some cases of dysplastic naevi and melanoma, and to this end any incompletely excised ‘dysplastic naevus’ must be re-excised
• Immunoflourescense – please see the section on immunology
• Cultures of skin biopsies – some organisms such as mycobacteria and leishmaniasis are best cultured from skin biopsies

The teaching of histology lies outside of the scope of this website. The best way to learn about histology is to attend local dermato-pathology and other MDT meetings. Or if you do not understand a histological result pick up the phone and speak to the local histopathologist or dermatologist

Patch tests – for the investigation of contact allergic dermatitis

Skin prick tests - mainly used to detect suspected latex allergy