In contact dermatitis the diagnostic method of choice is: (AIIMS May 2012)
1). Patch testing is used to document sensitivity to a specific antigen. In this procedure, a battery of suspected "allergens" with control is applied to the patient's back under occlusive dressings and allowed to remain in contact with the skin for 48 hours.
2). The dressings are then removed, and the area is examined for evidence of delayed hypersensitivity reactions such as erythema, edema, or papulovesicles.
3). This test is best performed by physicians with special expertise in patch testing and is often helpful in the evaluation of patients with chronic dermatitis. (Reading is read at 0, 2, 4 days)