Patch test is read after: (AIIMS May 2014)
1). Patch testing is used to confirm the diagnosis of allergic contact dermatitis.
2). In this test, a battery of suspected allergens along with control is applied to the patient's back under occlusive dressings and allowed to remain in contact with the skin for 48 hours.
3). The dressings are then removed, and the area is examined for delayed hypersensitivity reactions (such as erythema, edema, or papulovesicles). 2nd reading is taken on Day 4 to rule out false +ve irritant reaction.