Instituting an exclusion diet for 2 - 6 weeks, and following it up with a planned and intentional re-introduction of the diet, is important for
the diagnosis of a food allergy when a cause-and-effect relationship between ingestion of food and symptoms is unclear.
Food may be re-introduced after (short-term) exclusion diets for mild-to-moderate non-immunoglobulin E (IgE)-mediated conditions in
a safe clinical environment or cautiously at home. However, patients who have had an IgE-mediated immediate reaction to food, a previous
severe non-IgE-mediated reaction or a long period of food exclusion should not have a home challenge, but rather a formal incremental
food challenge protocol in a controlled setting.
An incremental oral food challenge (OFC) test is the gold standard to diagnose clinical food allergy or demonstrate tolerance. It consists
of gradual feeding of the suspected food under close observation. It should be done by trained practitioners in centres that have experience
in performing the procedure in an appropriate setting.
An OFC must be performed in a setting where resuscitation equipment is available in the event of a severe anaphylactic reaction. OFCs are
terminated when a reaction becomes apparent. Standardised and pre-set criteria are available on when to discontinue challenges. Patients who
tolerate the full dose ‘pass’ the challenge and are advised to eat a full portion of the food at least twice a week to maintain tolerance. Those who
have reactions have ‘failed’ the challenge, should avoid the food, receive education and implement risk-reduction strategies where appropriate.
Patients should be observed for a minimum of 2 hours following a negative challenge and for 4 hours after a positive one.