Practice Rational Testing

Diagnosis of immediate food allergy

BMJ 2014; 349 doi: http://dx.doi.org/10.1136/bmj.g3695 (Published 11 July 2014) Cite this as: BMJ 2014;349:g3695
  1. Cathal Steele, specialty registrar 1,
  2. Niall Conlon, academic clinical lecturer21,
  3. J David Edgar, consultant immunologist1, honorary senior lecturer 2
  1. 1Belfast Trust Regional Immunology Service, Royal Hospitals, Belfast BT12 6BA, UK
  2. 2Centre for Infection and Immunity, Queen’s University Belfast, Belfast, UK
  1. Correspondence to: C Steele cathal.steele{at}belfasttrust.hscni.net

Key points

  • Before you consider allergy testing, take a focused history: ask about the suspected allergen, symptoms, and their timing in relation to suspected allergen exposure

  • Skin prick and specific IgE testing should be used to diagnose immediate food allergy only when the clinical history supports this

  • Select only the specific allergens suspected in the clinical history. The use of specific IgE food panels or a blanket screening approach is likely to yield positive results that are difficult to interpret

  • Positive results of specific IgE or skin prick testing without clinical reactivity denote sensitisation and dietary restriction is not recommended

  • Unnecessary dietary restriction increases the risk of nutritional deficiencies and parental/patient anxiety

A 10 month old girl with a history of eczema was brought to the emergency department with urticaria and angioedema without respiratory or circulatory features to suggest anaphylaxis (see glossary). Ten minutes before the symptoms appeared she had eaten some lightly cooked (scrambled) egg. The emergency department doctor administered oral antihistamines and instituted close clinical monitoring. Within 30 minutes symptoms had resolved, and the child was discharged after a six hour period of observation. The doctor explained the likely diagnosis of an egg allergy and recommended avoidance of foods containing egg. An appointment with the GP to consider further investigation or onward referral to a paediatric allergy service was advised. When consulting their GP the next day, the parents asked about tests to confirm egg allergy and whether an adrenaline auto-injector was necessary.

What is the next investigation?

Before allergy testing is carried out a focused history is essential (box 1). Urticaria and angioedema (see glossary) are compatible with an immediate hypersensitivity reaction to food but can also occur spontaneously without any allergic trigger. In immediate (IgE mediated) food allergy the allergen exposure should have a close temporal relation with the onset of symptoms.1 …

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