Our experienced dermatologists often diagnose skin conditions 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 necessary to monitor the effects of systemic treatments.
- Standard skin or wound swabs have a cotton-tip on a plastic shaft and are typically placed in transport medium for routine bacterial culture, and if appropriate, antibiotic sensitivities are done.
- Skin scrapings, nail clippings and extracted hair are treated with potassium hydroxide (KOH) and examined by direct microscopy before being plated out for fungal culture. An interim report may describe hyphae, arthrospores and mycelia typical of dermatophyte or yeast infections. Culture results and the specific organisms identified are reported about 4 weeks later.
- Skin specimens in a small amount of sterile saline may also be processed for gram stain, microscopy and culture, including low-temperature culture for atypical mycobacteria and identification of organisms such as leishmaniasis and deep fungal infections.
- Neutrophilia is typical of infection but may also accompany severe inflammatory disorders including generalised pustular psoriasis, and neutrophilic dermatoses such as sweet syndrome or pyoderma gangrenosum.
- Eosinophilia is associated with atopic eczema, scabies, bullous diseases and lymphoma. It can be quite nonspecific in patients with erythroderma.
- Lymphocytosis is associated with viral infections and certain bacterial infections such as tuberculosis and syphillis.
Renal, hepatic, thyroid and iron may be evaluated in patients with generalised body itching or pruritus, vasculitis or systemic symptoms.
Blood glucose and glycosylated haemoglobin detect and monitor diabetes, which may be of relevance in infection, or skin diseases associated with metabolic syndrome.
Antinuclear and extractable nuclear antigen antibodies and tissue autoantibodies are assessed in patients with suspected connective tissue or autoimmune disease.
Proteins, including immunoglobulins, cryoproteins and complement, are assessed in patients with vasculitis or connective tissue disease.
Specific serology is requested for infections, eg, hepatitis B, Hepatitis C, HIV and syphilis.
Additional tests in vasculitis include anti-neutrophil cytoplasmic antibodies (ANCA), antiphospholipids, thrombophilia screen.
Hormonal tests are occasionally arranged in females with acne, hirsutism and androgenic alopecia if symptoms indicate these tests are warranted, or if virilism is present.
Urinary and faecal or serum porphyrins are requested in patients that may have a cutaneous porphyria.
Determination of allergy requires a careful history and examination, and testing should have a specific question in mind.
Skin 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.
Skin patch tests are undertaken by specialists for patients with suspected contact allergic dermatitis they detect delayed hypersensitivity reactions. Patients should have a chronic or relapsing dermatitis.