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Diagnostic Techniques

»	What is the most sensitive office laboratory test for diagnosing dermatophyte infections of the skin?
»	How is a KOH examination performed?
»	What laboratory tests are useful for diagnosing tinea capitis?
»	What is a Wood’s light or lamp? How is it useful in skin diseases?
»	Name common culture media used for isolating dermatophytes.
»	Describe a simple test for tinea versicolor other than a KOH preparation.
»	What is a Tzanck preparation or smear?
»	What is the best method of diagnosing scabies?
»	How do you diagnose mite bites acquired from an animal?
»	How do you diagnose lice infestation?
»	What is the diagnostic test of choice for a patient presenting with a suspected syphilitic chancre on his penis?
»	How is secondary syphilis diagnosed?
»	How long do serologic tests for syphilis remain positive?
»	In patients with symptomatic gonococcal urethritis, how efficacious is a Gram stain of the exudate in comparison to a culture utilizing selective media for gonococcus?
»	What is the best way to diagnose allergic contact dermatitis?
»	How are patch tests applied?
»	In what diseases is a skin biopsy helpful?
»	When are shave biopsies indicated?
»	What are the indications for punch biopsies?
»	Describe the indications for an excisional or incisional biopsy.
»	Define and describe direct immunofluorescence of the skin.
»	Name some skin diseases in which DIF is helpful in making a diagnosis.
»	How does indirect immunofluorescence of the skin differ from direct immunofluorescence of the skin?
»	Is ELISA ever used for the diagnosis of immunobullous disease?
»	How are bacterial skin cultures performed, and when are they useful?

What is the best way to diagnose allergic contact dermatitis?

The diagnostic test of choice is a properly applied and correctly interpreted patch test. Contact dermatitis is divided into irritant or allergic subtypes. Allergic contact dermatitis is immunologically mediated and is an acquired sensitivity that affects only certain individuals. Irritant contact dermatitis is not immunologically mediated and is due to chemical damage of the skin. For example, excessive hand washing or exposure to battery acid will involve almost everyone exposed in such fashion.

Goossens A: Recognizing and testing allergens, Dermatol Clin 27:219–226, 2009.