Food challenges are performed to answer a variety of questions and play a vital role in the evaluation and management of patients with histories suggestive of food allergy. Indeed, their necessity is supported by studies revealing that more than half of patients with histories of adverse reactions to a food fail to react during blinded challenges to that food. There are a number of reasonable explanations for this that underscore the importance of food challenges.
Given the possibility of severe reactions, food challenges should only be performed in a medical setting with the necessary medications, equipment, and personnel experienced in the treatment of severe allergic reactions (anaphylaxis). Decisions about who should be challenged are reached only after a thorough evaluation and discussion of the risks and benefits with the patient and their family.
Few procedures in medicine answer a posed clinical question as directly as a properly performed food challenge. The information obtained can be life-altering.
Four Primary Reasons
There are four primary reasons for doing a food challenge:
1. Determine whether the wrong food is suspected as the cause of symptoms.
Inaccurate or misleading assumptions about which specific food is to blame can be based on history, skin testing, and lab testing results. Contamination of a food by other allergens is one way the history may lead to inaccurate conclusions. For example, a child having reacted to a french fry cooked in peanut oil might be suspected of being allergic to peanut when the actual cause of the reaction was fish protein from fish fried in the same oil. Or, sometimes the reaction is caused by a nonfood contaminant such as latex proteins deposited on foods by handlers wearing latex gloves. A reaction to dust mites in mite-contaminated baked goods is another example.
Differences between how patients react to allergens in a testing environment compared to how they react in ‘real life' may lead to inaccurate conclusions as well. Sometimes the food responsible for the reaction is not apparent from skin testing or laboratory testing. For example, a patient may have a positive skin test to several suspected foods and food challenges may be necessary to determine which, if any, of the foods is the culprit. Determining which food actually caused the reaction is necessary to aid in preventing future reactions and to avoid needlessly eliminating foods from the diet.
2. Prove that a food is NOT the cause of symptoms.
An example is a patient who has been mislabeled as allergic to one or more foods despite an unconvincing history or suspicious skin test or laboratory test results. We often see patients who unfortunately have had broad food panels obtained, which can give multiple, falsely positive results, leading to unecessarily restrictive diets. Giving the food under medical supervision reassures patients that they can eat the food safely.
Furthermore, sometimes the reactions are not related to food but are brought on by other things such as medications, toxins, parasites, allergen exposures by inhalation or contact, viral illness, exercise, or panic.
3. Verify whether a patient has outgrown food allergies.
Many children born allergic to milk, egg, wheat or soy outgrow their food allergies by their third to sixth birthday. Studies have also shown that about 20 percent of children with allergic reactions to peanut and about 10 percent of children with allergic reactions to tree nuts may outgrow their sensitivity. A carefully performed food challenge can safely document when the food can be returned to the diet or at least when the likelihood of a significant reaction is drastically reduced.
4. Discover the degree of sensitivity.
Discovering the degree of sensitivity is another reason for performing food challenges, although this is the least common of the above reasons why we perform food challenges.
Some patients, or their families, become concerned that exposure to even tiny amounts of a food might cause a life-threatening reaction. These concerns occasionally interfere with participation in normal activities and can lead to social isolation.
Although some patients are very sensitive, others find that more of the food than was expected could be tolerated without a severe reaction - even though positive skin tests and histories may suggest otherwise. This can be a relief for patients who have avoided activities out of concern for the possibility of extreme sensitivity. Alternatively, some patients are found to be more sensitive than was previously suspected. In this case, the importance of strict avoidance, as well as being thoroughly prepared to treat severe reactions, is reinforced.