This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Dental
In contact dermatitis the diagnostic method of choice is 
Select and explain. 
A. Patch test, B. Skin biopsy, C. Intradermal test, D. Tzanck test
A: Patch test
Answer: A: Patch test 
Explanation: 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. The dressings are then removed, and the area is examined for evidence of delayed hypersensitivity reactions such as erythema, edema, or papulovesicles.. This test is best performed by physicians with special expeise in patch testing and is often helpful in the evaluation of patients with chronic dermatitis. (Reading is read at 0, 2, 4 days)