Final answer:
A skin patch test should be done at least 24 hours before the actual procedure to ensure safety against allergic reactions, with results usually read in 48-72 hours for tests such as the Mantoux test for tuberculosis.
Step-by-step explanation:
The skin patch test, often referred to as a predisposition test, is a precautionary measure to ensure that an individual does not have an allergic reaction to certain substances they may be exposed to during a procedure. According to health guidelines, the skin patch test should be done at least 24 hours before the actual procedure. This time frame allows for the identification of delayed allergic reactions, which could manifest as redness, swelling, or hardness at the test site. It is important for this test to be read properly, which, in the case of a Mantoux skin test for tuberculosis, would be in 48-72 hours post-application to determine whether there has been a positive result, as indicated by specific signs and measurements at the site of injection.