Laboratory Tests and Ancillaries
Microscopy
Scabies_Diagnostics 1
The diagnosis of scabies is confirmed by microscopic identification of the mites, eggs, or mite feces. The specimen should be taken by scraping the burrows or the newest lesions without excoriations and eczematization. A drop of mineral oil should be placed on the lesion and then scraped with a sterile #15 surgical blade and may be viewed directly under a light microscope. A 10% potassium hydroxide (KOH) solution may be used to decrease the amount of keratinic debris, which is helpful when diagnosing crusted scabies. Dermoscopy may be used as a guide for procurement of skin samples. When skin specimens are negative but a strong clinical suspicion remains, a successful trial of scabicide therapy may confirm the diagnosis. Transparent adhesive tape pressed onto the skin can also be used to obtain microscopic samples.
Dermoscopy
Scabies_Diagnostics 2
A handheld dermatoscope is used to visualize skin burrows, mites, and eggs on the patient’s skin instead of scrapings. The characteristic finding is a dark, triangular shape that represents the head of the adult female mite within a burrow (“delta wing” sign or “mini triangle" sign). Videodermatoscopy and reflectance confocal microscopy provide more detailed inspection of mites. Modified dermoscopy using ultraviolet light allows for easier visualization of the mite’s entire body, known as the “ball sign”.
Other Tests
Laboratory tests may reveal eosinophilia and elevated immunoglobulin E (IgE) levels. Digital photography is also an effective method for diagnosis and treatment response assessment.