Medical Definition of PATCH TEST. : a test for determining allergic sensitivity that is made by applying to the unbroken skin small pads soaked with the allergen to be tested and that indicates sensitivity when irritation develops at the point of application—compare intradermal test, prick test, scratch test. a test for determining allergic sensitivity that is made by applying to the unbroken skin small pads soaked with the allergen to be tested. See patch test defined for kids. ADVERTISEMENT.