Once food allergy symptoms have resolved, following a food exclusion in the diet, food challenges should be undertaken to find what is the specific allergenic food. Ideally, patients should be symptom free or stabilised prior to the food challenge.

History and/or diagnostic tests help determine the foods that should be evaluated by food challenges. This is best achieved with an elimination diet.
A number of medications should be avoided prior to a food challenge including antihistamines, beta-antagonists, theophylline, cromolyn and tricyclic depressants.
Foods may be masked in various infant formulas for young children or in elemental formulas, fruit juices, pureed foods, or meat patties for older children and adults.

There are three types of food challenges useful to perform an accurate diagnosis of food allergy:

• open food challenges;
• single blind;
• double-blind placebo-controlled food challenge (DBPCFC).

In open food challenges both the patient and the physician are aware of the food being challenge. They are made using an adapted infant formula and the challenge period is one week; both the doctor and the parent know that the given formula contains the protein under investigation.

In single blind the patient is unaware of the food being challenged, but the physician knows.

Finally, in double-blind placebo-controlled food challenge (DBPCFC) neither the patient nor the physician knows the contents of the challenge.
DBPCFC is considered as the “gold standard” and is the only truly reliable diagnostic test for adverse food reactions behind food allergies.
Double-blind placebo-controlled food challenge is also required in chronic disorders, such as atopic dermatitis or asthma, where patients who appear to have multiple food allergies or in situations in which patients’ perceptions may influence an accurate symptom evaluation.

The length of observation period is generally up to 2 hours for IgE-mediated reactions; however, if the patient history describes a more delayed reaction, a longer time may be required. Challenges to new foods may be conducted every 1 to 2 days.

Challenge tests should be supervised by the doctor and the dietitian: oral food challenges should be conducted in a clinic or hospital setting and only when trained personnel and equipment for treating systemic anaphylaxis are immediately available. The evaluation of many delayed reactions can be conducted safely on an outpatient basis.
The patient may be sent home after the first day of the open challenge if he/she remains symptom free. The challenge continues at the patient’s home where normal amounts of the infant formula are consumed per day. Patients record all the reactions on a form. If any adverse reactions appear the patient is reviewed at the hospital.

The food allergy diagnosis is confirmed 1 month after commencing the challenge.
The Elimination Diet in details…

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