An allergy skin test in which the allergen is put on a patch and then applied to the skin, such as at the back or on the arm, in order to detect the allergen that is capable of causing local allergic reaction on the patient
The patch test is an immunologic test that is used to detect the allergen causing the allergic reaction in a patient. It is carried out by a physician applying a patch containing the allergen to the skin of the patient. Typically, the patch is applied on the upper outer arm or at the back of the patient. After 48 hours, the area covered with the patch is compared with the uncovered skin surface. A positive result is determined when an erythematous reaction and the swelling are observed at the skin surface that contacted the allergen. The patch test is done on patients suspected of having an allergic contact dermatitis or with an atopic dermatitis.
The patch test is one of the allergy skin test methods for detecting hypersensitivity. However, it is a more sensitive test compared with the other allergy skin test methods. It can detect certain allergens that cannot be identified through skin prick test.