Food allergy diagnosis

Getting it right is important because otherwise people end up scared of foods, cut out different foods and risk nutritional/growth problems as well as aversion in the child. Having unproven food allergies also causes huge problems for schools and nurseries, and may lead to the public becoming sceptical of true allergy, with potentially disastrous consequences.

Getting it right can identify other potential allergies; it can help estimate risk of anaphylaxis; it can help with predicting whether the allergy is going to go away or not.

Allergy focused history

EATERS method –

  • Exposure – did they actually eat it!? Or was there clear skin contact? Perhaps from surface contamination?
  • Allergen (suspected) – one of the common ones? Although you can be allergic to pretty much anything, it is really rare to have an isolated rare food allergy.
  • Timing – type 1 is immediate (within 15 minutes, rarely up to 1hr after) and then settles even without treatment within 24 hours. Rare to fluctuate.
  • Environment – home (usually during weaning)? Outside home? Co-factors (infection, medicines, exercise, sleep deprivation) come in here.
  • Reproducible – consistent reactions with exposure? May have had before with type 1 allergy but often on trying for the first time, and won’t have had recently. Milk/egg different, of course…
  • Symptoms – type 1 vs non type 1. Some overlap of course.
[Mich Erlewyn-Lajeunesse, ADC 2019]

Other issues are age (adolescents with hay fever more likely to develop secondary pollen food syndrome type allergies), alpha-gal allergy can be delayed up to 3 hours; raw vs cooked food sometimes makes a difference; usually you already have eczema and family history of atopy.


At the end of history taking, you should have be able to assess probability of type 1 allergy. If low, you may wish to proceed straight to challenge (unless reactions sound severe). Otherwise testing may help confirm or refute.

If negative/equivocal on initial skin prick or specific IgE testing, do another test! Skin prick if negative/equivocal IgE, and vice versa.

IgE Component testing may give added information, esp where potential pollen co-sensitisation – best evidence (mostly in US population, however) for Peanut, Hazelnut, Cashew (respectively Ara h 2, Cor a 14, Ana o 3 – other components may give extra information in some cases). Jug r 1 v specific (walnut) but not v sensitive.


Challenge will be useful where results still equivocal – viz

  • Results positive but never eaten or history inconsistent
  • Results positive but possibly co-sensitivity without allergy
  • Food in alternative form might be OK eg baked

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