What is a food challenge?
An oral food challenge (OFC), or feeding test, is a medical procedure in which a food is eaten slowly, in gradually increasing amounts, under medical supervision.1
What are the reasons to perform an OFC?
OFCs are usually done when a careful medical history and allergy tests, such as skin and blood tests, are inconclusive. The OFC is a more definitive test because it will show whether the food ingested produces no symptoms or triggers a reaction.
What are open and blinded (masked) oral food challenges?
In clinical practice, most OFCs are performed openly, meaning that both the patient and the person administering the OFC know what food is being eaten; for example, eating peanut butter.
In blinded challenges, either the patient (single-blind), or both the patient and the medical personnel (double blind) do not know whether the “real” test food is being eaten or a fake food, known as placebo. For example, peanut flour may be hidden in a cookie while a similar looking and tasting cookie without the peanut flour is the placebo.
The double blind OFC is considered the best test since it reduces possible anxiety related reactions. Blinded challenges are rarely performed in clinical practices, and are usually done in research studies.2
What do I need to do in preparation to have an OFC?
You need to be in good health on the day of the test. Chronic allergic conditions such as asthma, atopic dermatitis (eczema) and allergic rhinitis (hay fever) have to be well controlled so they do not interfere with the interpretation of any symptoms.3 If you are sick on the day of the test, postpone it. You should also carry your usual medications and emergency medications with you so you have them for the trip to the doctor and back.
Do I have to stop any medications before having an OFC?
Yes. Antihistamines have to be stopped before the OFC since they might mask mild early symptoms. Ask your doctor how long you need to be off the type of antihistamine you are using. It may be difficult to stop allergy medications during an allergy season or in patients with significant eczema, therefore OFCs may need to be timed to avoid the seasons that cause problems.
As an alternative, medications other than antihistamines may be used, such as intranasal steroids, leukotriene antagonist or inhaled corticosteroids, in the 1to 2 week period before the OFC to minimize the discomfort caused by stopping oral antihistamines. If a person needs their asthma rescue medications around the time of the test, the test should be postponed. However, NEVER avoid using a needed emergency treatment such as epinephrine, antihistamines or inhaled asthma rescue medications just because you have an OFC scheduled. Treat the problem and postpone the test.
Who provides the food?
Talk to your doctor. Some may have you bring specific items, others may provide the food. Discuss your child’s food preferences. For infants, younger children or picky eaters, you may need to have several food options ready to minimize the possibility of food refusal for a picky eater. For example, soy may be tested as edamame, tofu, soy ice cream or soy milk.
For children, bring favorite serving dishes and utensils, and distractions such as toys, books, or homework.
What happens on the day of the test?
You may be instructed to avoid food or have a very light meal before starting. A physical examination and vital signs are done before starting and periodically during the test. The OFC starts with a small serving of the food and after a period of time, usually 15-30 minutes, if no symptoms are present, a slightly larger amount is eaten.
Before each subsequent dose, careful evaluation is performed to look for any symptoms. If symptoms occur, and the medical personnel judge that a reaction is happening, the feeding is stopped and medications are given as needed. Otherwise, the feeding continues until, typically, a meal sized portion is eaten.
What is the usual treatment in case of an allergic reaction during an OFC?
Most food challenges that result in a reaction trigger skin or stomach symptoms. The symptoms are usually mild because the testing is done gradually with small amounts of food at the start, and feeding is stopped at the onset of symptoms. Most often, antihistamines are given for these mild symptoms. If there are more severe symptoms, treatments can include epinephrine and other medications.
How long do I have to stay after the feeding is over?
If there were no symptoms during an OFC, usually patients are discharged from the office within 1to 3 hours of completing the feeding. In case of allergic symptoms, the patient is typically watched for at least 2 to 4 hours from the time symptoms go away or improve, with longer observation periods required for patients with more severe reactions.
Are OFCs different for different forms of food allergy?
Most food allergies lead to symptoms soon after the food is ingested. However, some forms of food allergy are delayed. For example, in food protein-induced enterocolitis (FPIES), symptoms typically do not begin for at least 2 hours and so the feeding is performed faster and the observation time is longer than for typical allergies. The dosing and observation time for an OFC can be adjusted to address an individual patient’s pattern of reaction.
What are the post-test instructions?
If the OFC did not cause symptoms, the patient is recommended to start regular consumption of the challenge food at home the following day. It is usually advised to make the food a routine part of the diet. Having symptoms after a “passed” OFC is uncommon.
If the OFC resulted in an allergic reaction, then continued avoidance is recommended.
What are the OFC risks?
The risks of OFC include an allergic reaction including anaphylaxis. There is no evidence that having an allergic reaction during an OFC makes future reactions worse or prolongs allergy in children.
What are the benefits?
The benefits include the nutritional and social benefits of being able to expand the diet if the food is successfully eaten without symptoms. However, even if the food triggered a reaction, the benefit is knowing that the food is truly a problem and needs to be avoided to maintain health.
1. Boyce JA, Assa'ad A, Burks AW, et al. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary of the NIAID-Sponsored Expert Panel Report. J Allergy Clin Immunol 2010;126:1105-18.
2. Sampson HA, Aceves S, Bock SA, et al. Food allergy: A practice parameter update-2014. J Allergy Clin Immunol 2014.
3. Nowak-Wegrzyn A, Assa'ad AH, Bahna SL, et al. Work Group report: oral food challenge testing. J Allergy Clin Immunol 2009;123:S365-83.
Additional information about food allergies.
This article has been reviewed by Thanai Pongdee, MD, FAAAAI