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

Strict elimination of the implicated food or foods is the logical consequen ce of the diagnosis of food allergy. Such a decision cannot be taken withou t sufficent proof, in particular in infants and young children whose develo pment requires a varied diet. In routine practice, the diagnosis of IgE-med iated food allergy can be established in the following circumstances: 1) ra pid onset of anaphylactic symptoms after ingestion of a single, well-charac terised food, in a patient with positive prick tests and/or RAST to the foo d in question; 2) an oral syndrome after ingestion of fruits and/or vegetab les in a patient with pollen allergy; 3) patients whose adverse reactions h ave totally and durably disappeared after an adequate elimination diet for at least six months. If the symptoms are equivocal, labial food challenge i s indicated to clarify the diagnosis: anaphylactic reaction which can be li fe-threatening if the allergen responsible cannot be identified by prick-te sts and/or dosage of specific serum IgE; confirmation that the allergy is c ured. Oral challenge tests should not routinely be used in patients with at opic dermatitis who have a clear and recent history of food allergy associa ted 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 neg ative RAST are little likely to have IgE-mediated food allergy; oral challe nge can be useful to exclude the diagnosis when the parents are convinced t he child has an allergy ("food neuroses"). Double-blind oral food challenge tests are indispensable for any clinical study, especially those evaluatin g new treatments. Before carrying out an oral challenge, every precaution m ust be taken. The informed consent of the patient and his/her family is ind ispensable, and their understanding must be ensured. Elementary prudence re quires 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 respo nsibility of the prescribing physician. Several teams are attempting to dev elop alternative techniques to oral challenge because of the potentially se rious adverse reactions incurred. (C) 2000 Editions scientifiques et medica les Elsevier SAS.