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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 most sensitive office laboratory test for diagnosing dermatophyte infections of the skin?

Microscopic examination of a potassium hydroxide (KOH) preparation of scrapings taken from the affected area is the most sensitive office laboratory test. A study of 220 specimens examined by both KOH and culture demonstrated positive KOH preparations and positive cultures in 45% of samples, a positive KOH preparation and negative culture in 52% of samples, and a negative KOH preparation and a positive culture in only 3% of samples. However, cultures can be useful because other studies have shown a 5% to 15% increase in positive specimens by culturing KOH-negative materials. Moreover, it is important to realize that the diagnostic accuracy of the KOH preparation depends on the skill of the individual performing the test.

Lefler E, Haim S, Merzbach D: Evaluation of direct microscopic examination versus culture in the diagnosis of superficial fungal infections, Mykosen 24:102–106, 1981.