## Investigation of Choice for Scabies Confirmation **Key Point:** Microscopic examination of scrapings from burrows is the gold standard diagnostic test for scabies, with sensitivity of 60–80% when performed correctly. ### Why Scrapings Under Microscopy? 1. **Direct visualization of organisms** — Allows identification of the *Sarcoptes scabiei* mite, eggs, feces (scybala), or eggshells 2. **High specificity** — Positive result confirms diagnosis; false positives are rare 3. **Practical and cost-effective** — No specialized equipment required; can be done in outpatient clinic 4. **Standard technique:** - Select an unscratched burrow (preferably interdigital space, wrist, or genitalia) - Apply mineral oil or potassium hydroxide (KOH) to soften the burrow - Scrape with a blunt blade or needle until slight bleeding occurs - Transfer material to a glass slide - Examine under low power (10× or 40×) for mites, eggs, or feces ### Diagnostic Findings on Microscopy | Finding | Appearance | |---------|------------| | **Mite** | 0.3–0.4 mm, oval, 4 pairs of legs | | **Eggs** | Oval, 100–150 μm | | **Feces (scybala)** | Brown, granular material | | **Eggshells** | Empty, translucent | **High-Yield:** Even a single mite, egg, or fecal pellet on microscopy confirms the diagnosis. Absence does not rule out scabies (sensitivity ~60–80%), but presence is diagnostic. **Clinical Pearl:** If microscopy is negative but clinical suspicion remains high (e.g., family members affected, typical distribution), treat empirically — diagnostic certainty should not delay therapy in symptomatic patients. ### Sensitivity Considerations - **Sensitivity 60–80%** — Depends on: - Correct site selection (burrows yield higher sensitivity than papules) - Adequate scraping technique - Number of mites present (lower in treated or partially treated cases) - Examiner experience [cite:Irvine's Dermatology 10e Ch 31] 
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