In a food allergy blood test, a blood sample is collected from a vein in your arm. A lab then tests this blood sample for food-specific IgE antibodies in order to discover potential food allergies. When your immune system identifies an allergen in your circulation, it produces IgE antibodies. These antibodies identify the allergen when they bind to it later. Blood samples are usually taken after an allergic reaction has occurred or may be taken before an event triggers a response. The sample is then sent to a laboratory where the IgE antibody level is measured. The sensitivity of a testing method can be determined by repeating the test on several different occasions and looking at how often positive results are obtained. If negative results are rarely reported, the test may not be very sensitive. If positive results are frequently reported when the patient does not have the disease, the test may be reporting false positives due to other factors such as the presence of IgE antibodies not related to the disease process. A highly sensitive test would detect positive results even when the patient does not have the disease so that appropriate action could be taken. For example, a doctor might want to know if a new medication causes symptoms similar to those caused by insect stings. To do this, the doctor could give the patient a dose of the medication and watch to see if any reactions occur. If no reactions occur, the patient does not have an allergy to the medication and another can be chosen.