Dermatological investigations and tests

Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, December 2016.

An experienced clinician can often diagnose a skin condition without the need for investigations. However, at times, skin swabs, scrapings and nail clippings, biopsies, and blood samples are sent to the laboratory, and allergy testing or imaging is arranged. Investigations may also be used to monitor the effects of systemic treatments.

Microbiology

Histopathology

Haematology

Other blood tests

Allergy tests

Determination of allergy requires a careful history and examination, and testing should have a specific question in mind.

Prick tests

Prick tests for immediate hypersensitivities are not very useful in the investigation of skin disease. These tests are sometimes undertaken in patients with suspected contact urticaria or latex allergy. They are not useful in atopic dermatitis or acute/chronic spontaneous urticaria.

Patch tests

Patch tests are undertaken by specialist clinics for patients with suspected contact allergic dermatitis; they detect delayed hypersensitivity reactions. Patients should have a chronic or relapsing dermatitis.

Imaging

Radiological examinations

X-rays, CT scans, MRI scans and ultrasound tests are not routinely requested in dermatology, but may be arranged for systemic symptoms or monitoring treatment.

Wood light examination

Exposure to long wavelength UVA emitted by a Wood lamp is mainly used to investigate pigmentary disorders and chronic superficial skin infections such as pityriasis versicolor, where fluorescence supports a specific cause.

Digital dermatoscopy

Digital dermatoscopy is digital imaging of skin lesions under dermatoscopy. Ideally, these are accompanied by macroscopic and location images. Dermatoscopic images can be taken using a variety of dermatoscopes, adapters and video and still cameras using contact and non-contact, polarised and unpolarised systems.

Mole mapping is a system in which the location of melanocytic naevi is mapped to a mannequin, total body photographs are taken, and macroscopic and digital images are recorded for lesions of clinical concern. The procedure is repeated at intervals to monitor patients with high risk of melanoma, particular if they have many naevi or naevi with an unusual appearance.

Other

Optical coherence tomography and reflectance confocal microscopy are in-vivo techniques for cutaneous diagnoses. They are mainly used in research centres. 

Related information

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