Skin scraping

Role

Skin scraping for microscopy (potassium hydroxide preparation) is a rapid, bedside investigation for suspected superficial fungal infection or scabies - providing an immediate answer without the delay of culture or biopsy
A very commonly performed, low-cost point-of-care test given the high prevalence of superficial fungal skin infections and the diagnostic value of confirming scabies before committing to treatment

Fungal skin infection: scraping from the active, scaling edge of the lesion, examined under potassium hydroxide preparation for hyphae, confirms dermatophyte infection and distinguishes it from other scaly rashes (psoriasis, eczema) that can mimic tinea clinically
Scabies: scraping from a burrow (classically finger webs, wrists) examined under microscopy for mites, eggs, or faecal pellets confirms diagnosis, though sensitivity is imperfect and a negative scrape does not exclude scabies with a compatible clinical picture

Bedside/rapid: immediate result at the point of care, unlike fungal culture (which takes 1-3 weeks) - scraping and culture are complementary rather than interchangeable, with scraping giving speed and culture giving species identification when needed
Technique matters: scraping the active scaling edge (not the centre) for suspected tinea, and targeting a visible burrow for suspected scabies, meaningfully affects diagnostic yield

A positive result confirms diagnosis and guides specific treatment (topical/systemic antifungal for tinea, scabicide for scabies with contact treatment); a negative scrape with strong clinical suspicion should prompt repeat sampling or empirical treatment rather than confidently excluding the diagnosis, given imperfect sensitivity

Tinea corporis/cruris/pedis (dermatophyte infection), scabies (mite infestation, contact tracing implications), psoriasis/eczema (key mimics excluded by a negative fungal scrape)

Scraping technique (active edge for tinea, visible burrow for scabies) directly determines diagnostic yield - a poorly targeted scrape can produce a false-negative result even with genuine active disease, so technique should be actively taught rather than assumed

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