History and physical examination

As with virtually all medical disorders. the diagnostic approach to a patient with a suspected adverse food reaction begins with the history and physical examination. Depending on the information derived from these initial steps, various laboratory studies may be helpful [see Table 5].

In cases of suspected adverse food reactions. the value of the history depends largely on the patient’s recollection of symptoms and on the examiner’s ability to differentiate disorders provoked by food hypersensitivity from disorders with other etiologies. The history may be directly useful in diagnosing food allergy involving acute events (e. g. anaphylaxis after eating fish) but is not always reliable: in many series, less than 50% of reported allergic reactions to food could be substantiated by a double-blind, placebo-controlled food challenge (DBPCFC).3,7 In chronic disorders such as atopic dermatitis, the history is typically an unreliable indicator of the offending allergen.

Several items of information are important in establishing that an allergic reaction to food occurred: (1) the type of food suspected to have provoked the reaction; (2) the quantity of the food ingested; (3) the length of time between ingestion and onset of symptoms; (4) the specific symptoms provoked; (5) whether similar symptoms developed on other occasions when the food was eaten; (6) whether other factors (e. g. exercise) were involved in the episode; and (7) the length of time since the last reaction.

Although any food may cause an allergic reaction, only a few foods account for 90% of such reactions. In children, these foods are eggs, milk, peanuts, soy, and wheat (and in Scandinavian countries, fish).