When testing for food allergies, we use an approved testing system which measures an IgE reaction. IgE is an antibody that reacts when exposed to an allergen. Your sample is exposed to a number of food and non-food items to determine the substances that would trigger an inflammatory response in your body were you to ingest or come into contact with it. A response would trigger symptoms in your body.
The NHS use IgE blood testing as well as skin prick tests, patch tests and food challenge testing to diagnose allergies.