Once the range of possible allergens has been narrowed down with a test for the detection of food-specific IgE antibodies (skin prick testing or blood tests), a food challenge test can be used to confirm or exclude allergy.
A food challenge test involves giving the patient increasing doses of the suspected allergenic food, allowing ample time between doses for a response to occur. A medical specialist with a high degree of knowledge about food allergy must always supervise the performance of the challenge test. The challenge must be conducted within a medical facility with equipment and staff to deal with possible life-threatening reactions. A patient who has had a genuinely life-threatening allergic reaction, like anaphylaxis, should not be challenged with the food that caused it unless the challenge starts with an extremely low dose.
Before a food challenge test, patients must avoid the suspected food(s) for at least 2 weeks. Regular antihistamine medication is also withdrawn. When performing the test the doses should be increased very gradually until a normal serving of the foods has been eaten. A negative challenge is valid only if no symptoms are observed following exposure to the problem food in a dose equivalent to a normal serving. The medical team will observe the patient for symptoms for up to several hours after the challenge.
For older children and adults, challenges can be conducted in a double-blind manner with a placebo control (double-blind, placebo-controlled, food challenge, DBPCFC). In this test, neither the patient, nor the investigator knows whether the food preparation being given contains the specific allergen or a placebo. The suspected allergen or placebo will be hidden in a food matrix (recipe) consisting of foods normally tolerated by the patient.
Even though the DBPCFC test is the gold standard in food allergy diagnosis, the test may produce false negative results. The challenge procedure usually cannot reproduce the exact circumstances under which the patient experienced the adverse reaction.
When challenging infants and small children it is not necessary to hide the food. An open challenge is the standard procedure in these age groups.