Diagnosing and managing food allergy in children.

The prevalence of food allergy in children in the UK is now around 5%. The number of children put on restricted diets by their parents because of presumed allergy is likely to be much higher. Accurate diagnosis of food allergy is essential in order to ensure that the correct foods are carefully avoided while safe foods are not excluded unnecessarily. IgE-mediated (immediate type) reactions are the result of mast cell degranulation leading to histamine release. The typical signs of lip swelling, urticaria and possible progression to respiratory compromise (anaphylaxis) are usually clearly described, occurring within minutes of exposure to the food. Non IgE-mediated (delayed type) responses tend to start 2-6 hours, occasionally longer, after exposure and cause less specific signs/symptoms, less obviously allergic in origin. Where an immediate type allergic reaction is suspected on clinical history, allergy testing should be performed to confirm the diagnosis. This could involve either skin prick testing or specific IgE blood tests. Results must be interpreted in the context of the clinical history. The mainstay of management is allergen avoidance. The child and carers also need to know how to recognise and treat any future allergic reactions. There should be a written emergency plan in place. The plan should include advice to take a fast-acting antihistamine if any accidental exposure and reactions occur. Where there is a history of anaphylactic reaction or ongoing asthma, adrenaline auto-injectors should be prescribed as these are the major risk factors for future severe reactions. Non IgE-mediated food allergy is most common in early infancy. The diagnosis of non IgE-mediated food allergy relies on a two-stage process: strict exclusion of suspected allergen(s), only one at a time; re-challenge with suspected allergen(s), one at a time, to see if symptoms recur.