Food allergies and diagnostic alternatives: labial food challenge, oral food challenge.

Strict elimination of the implicated food or foods is the logical consequence of the diagnosis of food allergy. Such a decision cannot be taken without sufficent proof, in particular in infants and young children whose development requires a varied diet. In routine practice, the diagnosis of IgE-mediated food allergy can be established in the following circumstances: 1) rapid onset of anaphylactic symptoms after ingestion of a single, well-characterised food, in a patient with positive prick tests and/or RAST to the food in question; 2) an oral syndrome after ingestion of fruits and/or vegetables in a patient with pollen allergy; 3) patients whose adverse reactions have totally and durably disappeared after an adequate elimination diet for at least six months. If the symptoms are equivocal, labial food challenge is indicated to clarify the diagnosis: anaphylactic reaction which can be life-threatening if the allergen responsible cannot be identified by prick-tests and/or dosage of specific serum IgE; confirmation that the allergy is cured. Oral challenge tests should not routinely be used in patients with atopic dermatitis who have a clear and recent history of food allergy associated with bronchial hyperreactivity, nor in patients with atopic dermatitis who after a severe allergic reaction have positive prick tests and/or RAST. On the contrary, children with negative prick tests to fresh foods and negative RAST are little likely to have IgE-mediated food allergy; oral challenge can be useful to exclude the diagnosis when the parents are convinced the child has an allergy ("food neuroses"). Double-blind oral food challenge tests are indispensable for any clinical study, especially those evaluating new treatments. Before carrying out an oral challenge, every precaution must be taken. The informed consent of the patient and his/her family is indispensable, and their understanding must be ensured. Elementary prudence requires preliminary placement of a venous line, in particular for "dangerous'' foods (peanuts, seafood, sesame). Food challenges must be carried out in a hospital setting by a trained team. They are carried out under the responsibility of the prescribing physician. Several teams are attempting to develop alternative techniques to oral challenge because of the potentially serious adverse reactions incurred. (C) 2000 Editions scientifiques et medicales Elsevier SAS.