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Editor,—True and perceived nut allergy is a problem that paediatricians are seeing ever more frequently and guidelines for adequate diagnosis are needed. We therefore published our experience of children presenting to a general paediatric clinic with this problem.1 In their letter O'B Hourihaneet al have some points regarding the methodology we used for the diagnosis of nut allergy2; we would like to comment on some of those issues.
The assumption that nut was the “only possible allergen” in a composite food was questioned. Although any allergenic food can cross contaminate other foods, severe or fatal allergic reactions are more likely following exposure to peanuts.3 Thus any child with a known anaphylactic reaction was excluded from an oral challenge on this basis. However the vast majority of children presented with non-specific symptoms where nut ingestion was implicated as the cause of their symptoms. Further investigation was warranted before a diagnosis of nut allergy could be reached.
Skin testing is known to be unreliable,4 and given the lifestyle implications some parents and children were unhappy to accept a diagnosis of nut allergy on the basis of serum IgE results alone. Under these circumstances oral challenge was offered as a diagnostic investigation.
Our protocol was also criticised for exposing children to only 2 g of nut when a minimum amount of 8 g should have been administered. The maximum amount administered to each child in our protocol was not 2 g, but rather a portion of the same foodstuff reported to have caused the allergic reaction. In addition, O'B Hourihaneet al,5 based on previous publications, have suggested that as little as 50 mg of peanut protein is needed in testing for allergic reactions.3 6 Children admitted for investigation were required to stay for at least one hour after testing; no child tested in this manner has subsequently returned with allergy to nuts.
True peanut and nut allergy is a devastating illness, but fortunately this is uncommon.7 8 The incidence of perceived food allergy within the UK population however is as high as 20%,9 and general paediatricians care for the majority of children with possible nut and other food allergies. Clearly treatment of these children without investigation is inappropriate and direct oral challenge has been advocated in some instances.4 Our key message remains unchanged—in certain circumstances within a controlled environment it is appropriate to consider oral challenge to obtain a definitive diagnosis of nut allergy.