Potassium hydroxide preparation and/or fungal culture to exclude tinea are often indicated for dermatitis of the hands and feet. This helps identify disorders such as tinea pedis.
No single diagnostic test is used for diagnosis of irritant contact dermatitis. The diagnosis rests on the exclusion of other cutaneous diseases (especially allergic contact dermatitis) and on the clinical appearance of dermatitis at a site sufficiently exposed to a suspected or known cutaneous irritant. Laboratory studies are generally of little value in proving a diagnosis of contact dermatitis. However, they may be of value in eliminating some disorders from the differential diagnosis.
Patch testing can be performed to diagnose contact allergies, but no patch test can prove that a cutaneous irritant is responsible for a particular case of irritant contact dermatitis.
Biopsies are of little diagnostic help in contact dermatitis. Most types of contact dermatitis show similar pathologic changes, and allergic and irritant contact dermatitis may not be distinguished with certainty in all cases. However, skin biopsy findings may serve to eliminate some conditions included in the differential diagnosis.
For more on the workup of contact dermatitis, read here.
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Cite this: William James. Fast Five Quiz: Compare Your Knowledge of Contact Dermatitis - Medscape - Jun 06, 2017.