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Food challenges
Your doctor also may consider a food challenge. In some cases, this test is the only way to make a definitive diagnosis of food allergy. The reason to perform a food challenge is to figure out if a suspected food is causing the symptoms by having the patient eat increasing amounts of that food under medical supervision until symptoms occur or the person tolerates a normal portion of the food.
Food challenges should be performed in a medical setting by experienced personnel with the medications and equipment needed for the treatment of anaphylaxis readily available. Before the food challenge, the doctor will review the patient's history. People who have uncontrolled asthma or who are otherwise ill should not participate in a food challenge. Doctors will check vital signs and lung function and perform a physical examination before starting a food challenge and during the test if the patient complains of symptoms.
Food challenges can be done different ways. In one type, called an open food challenge, both the patient and medical staff are aware that the patient is eating the suspected food. For example, a child receiving an open food challenge to egg might be given increasing doses of scrambled egg every 15 to 30 minutes until a whole egg is ingested.
In a single-blind placebo-controlled food challenge, the medical staff is aware of what the patient is being fed, but the patient is not. The suspect food is given as a hidden ingredient in another food.These types of trials are done to prevent the possibility of symptoms caused by patients being worried about eating a certain food. An egg trial done this way, for instance, would involve feeding small amounts of egg concealed in a different food, such as chocolate pudding. Each dose given to the patient could either contain concealed egg or not. However, the final dose of any food challenge is the open ingestion of a normal portion of the suspected food.
In a double-blind placebo-controlled food challenge, neither the patient nor the medical team conducting the test is aware of what the patient is being fed. (For the safety of the patient, at least one physician who is readily available but not directly involved in the test knows what the patient is ingesting.)
A food challenge generally takes between four and eight hours. If a child is having the challenge, a parent should be present for the duration of the challenge. Your doctor may ask you to bring in a specific food for a food challenge. If your child is being tested, you may also be asked to bring a favorite food in which to conceal the food being challenged.
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