Final answer:
A patch test, also known as a predisposition test (PD), is a diagnostic test used in dermatology to identify the cause of allergic contact dermatitis. It is performed by applying small amounts of different substances to adhesive patches, which are then applied to the skin for a specific period of time. The purpose of the test is to identify substances that may be causing an allergic reaction and determine the appropriate treatment.
Step-by-step explanation:
A patch test, also known as a predisposition test (PD), is a diagnostic test used in dermatology to identify the cause of allergic contact dermatitis. This test is performed by applying small amounts of different substances, such as chemicals or metals, to adhesive patches, which are then applied to the skin for a specific period of time, usually 48-72 hours.
The patch test is given on the patient's back or arms, where the skin is usually less sensitive. The purpose of the test is to identify substances that may be causing an allergic reaction, such as redness, itching, or swelling, when they come into contact with the skin. This information is important for determining the appropriate treatment and avoiding further exposure to the allergens.
For example, if a patient develops a positive reaction to nickel during a patch test, it indicates that they are allergic to nickel, and they should avoid wearing jewelry or clothing containing nickel to prevent future allergic reactions.