Final answer:
The raised area caused by an intradermal injection during hypersensitivity skin testing is called a wheal, and the surrounding redness is known as flare for type I hypersensitivity reactions; for type IV reactions, such as in the tuberculin test, a raised, hard area called an induration signifies a positive test.
Step-by-step explanation:
An intradermal injection is administered during skin testing for hypersensitivity reactions, such as allergies or tuberculosis screening. When the injection causes a reaction, the raised area seen is known as a wheal, with surrounding redness referred to as flare. This is characteristic of a type I hypersensitivity reaction, where the local vasodilation and increased permeability of blood vessels, caused by the release of histamine and other mediators, give rise to the wheal and flare within minutes of allergen exposure.
In the case of the tuberculin test for tuberculosis, which is a test for delayed hypersensitivity (type IV), the injection site might show a raised red area that feels hard, known as induration, typically appearing a couple of days after injection. This is due to an accumulation of activated macrophages, signifying exposure to the tuberculosis bacteria and a cellular immune response.