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Exams and Tests
There are many useful laboratory and special examinations which are helpful in the diagnosis of rash:
Sampling skin material and viewing under direct microscopy is a fast and simple way to help diagnose a rash. When a superficial fungal or yeast infection is suspected, viewing a superficial skin scraping with a potassium hydroxide prep can reveal fungal hyphae or budding cells.
Likewise, suspected bacterial infection can be evaluated by a Gram stain or nasal swab culture. Viral lesions typically caused by herpes simplex can be viewed under the microscope with a Tzanck smear which will show giant, multinucleate cells.
Blood tests can be helpful as well (for example, sudden onset of severe psoriasis may be associated with an HIV infection). Anti-streptolysin O (ASO) levels can be helpful in detecting a sudden onset of guttate psoriasis associated with a prior streptococcal throat infection.
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Rash - Effective Treatments
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