Oral Food Challenge

PERFORMANCE OF AN OFC - Consensus has not been reached on a uniform international protocol for performing oral food challenges. The protocol for oral food challenge (eg, dosing, frequency) may need to be varied to match clinical issues (eg, the history of the reaction pattern). In all challenges, the food is given in gradually increasing amounts.

Patient preparation - Informed consent should be obtained from the patient or guardian, and documented prior to beginning the challenge.

Patients need to avoid the suspected food(s) for at least two weeks before the OFC for suspected IgE-mediated allergy and several weeks longer for non-IgE-mediated reactions. Patients are not allowed to eat or drink for at least two hours prior to challenge.

Antihistamines, beta-agonists, beta-adrenergic blockers (including eye drops), and other medications that may either alter symptoms of a reaction or interfere with its treatment, should be discontinued for at least five half-lives (specific to each medication) prior to challenge. Patients should be instructed to bring their auto-injectable epinephrine to their appointment, so that it is available to them on the trip home after the test in the event of a delayed reaction.

Patients are advised to cancel the OFC if they are experiencing acute allergic symptoms or are otherwise ill at the time of their appointment. Patients with asthma should have a FEV1 of >70 percent of predicted prior to the challenge and should be stable on current therapy with no recent exacerbations. Infrequently, hospitalization may be necessary to treat severe or acute allergic disease and establish a stable baseline prior to challenges.

Children may be more cooperative if they are supplied with videos, games, and other distractions.

Location - Oral food challenges are almost always performed under direct medical supervision either in a clinic or hospital setting. Options for location include clinician offices, outpatient centers designed for procedures, inpatient hospital units, and monitored intensive care units. In unusual circumstances, foods may be gradually added back into the diet at home. This may be undertaken when specific IgE tests are negative, symptoms are mild or chronic, and there is little concern for potential anaphylaxis. Selection of an appropriate setting requires clinician judgment about risks and availability of advanced treatment of anaphylaxis. Oral challenges can elicit severe anaphylactic reactions in any setting. The physician must have appropriate training and be prepared with emergency medications and equipment to promptly treat such a reaction.

It is best to perform the challenge in a controlled setting (eg, hospital) if the patient is considered high risk (eg, positive test for IgE, previous anaphylactic reaction, history of asthma). It may also be prudent to have intravenous access prior to commencing challenges in patients with higher specific IgE levels or history of more severe reactions. Intravenous access should be strongly considered for all patients with food protein-induced enterocolitis syndrome (FPIES) undergoing a food challenge, since they are at risk for hypotension with reexposure to the food.

Dosing and timing - No single approach to dosing and timing is universally established for food challenges. Dose amounts and timing between doses should be adjusted to match the patient's history (eg, if days of ingestion are needed to elicit symptoms) or concerns about heightened sensitivity (eg, starting with minimal doses spaced out over longer periods of observation).

For example, a child with a history of atopic dermatitis flaring over days with milk ingestion, who carries positive IgE tests to milk and has been avoiding this protein for a year, may have an acute allergic reaction on the day of challenge or may experience a flare over days of ingestion. A graded oral food challenge under clinician supervision on the first day would evaluate the risk of an acute reaction, and, if tolerated, following the child's symptoms over the following days with milk added to the diet would evaluate for delayed responses.

The general approach is to select a regimen that is unlikely to result in a severe acute reaction by cautiously and gradually increasing the amount ingested (with the target cumulative dose of a meal-sized portion), while also considering time constraints.

For patients with past food reactions that occurred immediately after ingestion, doses are generally administered at 10 to 15 minute intervals over about 90 minutes, followed by a larger, meal-size portion of food a few hours later.

Starting dose - The starting dose should be low enough that it does not trigger a reaction in most patients.

One could argue for starting doses that begin under the thresholds reported to induce reaction, especially in patients who have a history of reacting to trace amounts of a food. However, threshold data are not available for most foods and the thresholds that are published vary.

Labial food challenge (placing the food on the lower lip for two minutes and observing for local or systemic reactions in the ensuing 30 minutes) has been suggested by some as a starting point before an oral food challenge.

Dose escalation - The total amount of food to be administered is given in escalating portions. As an example, for a milk challenge with the target dose of 100 mL (1 mL = 1 percent of the total dose), the doses could be: 1 percent, 4 percent, 10 percent, 20 percent, 20 percent, 20 percent, and 25 percent. However, a variety of other challenge regimens have been used, including lower starting doses, variations in the dosing increments, and different time intervals.

Monitoring - Patients should be examined carefully prior to an OFC to determine their baseline and to confirm that they do not have any current significant allergic signs/symptoms or an illness that would interfere with assessment and/or treatment of a reaction during the challenge. Vital signs are measured and signs and symptoms are recorded at baseline, prior to each dose, and at set intervals after the final dose. Assessments are made for symptoms affecting the skin, cardiovascular system, and gastrointestinal and respiratory tracts.

Children may become suddenly quiet or assume a fetal position prior to exhibiting more objective symptoms. Early indications of a reaction can include subtle signs such as moving the tongue in the mouth to rub an itchy palate, or ear pulling as an indication of itching. Oropharyngeal itching or pain often precedes objective symptoms. Children with atopic dermatitis may display an eczematous flare.

Discontinuing a challenge - Challenges are terminated when a reaction becomes apparent (eg, new objective symptoms or an increase in objective symptoms over baseline). Expert judgment is needed about whether or not to discontinue a challenge if symptoms are not clear. Generally a challenge is discontinued if subjective symptoms are repetitive or prolonged.

Following a negative oral food challenge in which the allergen was administered in a form not normally eaten (eg, peanut flour or powdered egg), it is essential to perform an open challenge with a meal-size portion of the food in the state in which it is normally ingested (eg, peanut butter or boiled egg). This is done to ensure that the processing of the allergenic food for challenge did not alter the allergen and to confirm the negative result.

Medical treatment for a reaction - Medications are given as needed to treat allergic or anaphylactic reactions. Generally, antihistamines are given at the earliest sign of a reaction. Epinephrine and other treatments are given if there is progression of symptoms or any potentially life-threatening symptoms.

Severe allergic reactions are an uncommon outcome of oral food challenges in children when typical criteria are used in deciding to proceed with a challenge. These severe reactions more commonly occurred in older children and in children challenged to peanut or tree nuts.

Full medical therapy (eg, epinephrine, antihistamines, intravenous fluids, oxygen, vasopressors, and H2-blockers), materials for resuscitation (ie, intubation), and personnel who can manage anaphylaxis should be immediately available. Doses for all rescue medications should be calculated in advance of challenges.

Observation following challenge - After a negative oral food challenge, we typically observe a patient for one to two hours. It is possible to have later onset symptoms, and we extend this period if the history suggests delayed reactions or if prior reactions were severe. We inform the patient not to eat more of the test food that day and to report and treat any symptoms. The food is added to the diet the next day if no delayed symptoms are reported.

Following a positive challenge, we observe patients for a minimum of two hours past resolution of mild symptoms that required minimal treatment and at least four hours for more significant reactions.

Post-challenge counseling - Patients who tolerate a challenge require counseling about how to introduce or reintroduce the food. Some patients and parents may continue to be fearful about eating the food, despite a negative challenge. This can result in continued avoidance. As noted above, avoidance or infrequent exposure may result in resensitization to the allergen. It is therefore important to encourage at least weekly or monthly ingestion of the specific food. Patients should be asked at subsequent visits about regular ingestion of the former allergen. A repeat challenge may be required in patients who have continued to avoid the food.

Patients who have had a negative OFC to one allergen may have remaining food allergies. These patients must be cautioned specifically about cross contamination by foods that are commonly associated with the food that they are now able to ingest.

Some patients may wish to continue carrying epinephrine even when there are no remaining food allergies. Patients may be advised to continue to have epinephrine available until it is clear that the food is tolerated as a routine part of the diet.

Patients who have failed the OFC can be partly consoled to know that their hard work at avoidance was necessary. Though reactions may vary and strict avoidance is typically advised, knowledge about the dose causing symptoms may provide helpful information to patients and families. Review of food avoidance measures is also helpful. The nutritional impact of food avoidance should be reevaluated.