Gold standard is double blind challenge, but who has time for that? And dangerous!

Mostly based on history – combination of characteristic features without other, more likely, explanation.

EAACI guidance 2023 says where type 1 allergy suspected (signs/symptoms but also timing and consistency of reaction):

• Do skin prick testing and/or specific IgE testing as first line
• After that, if still doubt then for peanut, hazelnut or cashew, if in doubt do component tests Ara h 2, Cor a 14, Ana o 3 respectively (if available) – otherwise do skin prick or IgE if not done already.
• Where peanut or sesame allergy still in doubt, do basophil activation test (BAT – if available – nowhere in Scotland, as far as I know)
• “Reassessment of food allergic children, at regular intervals, depending on age, food and patient’s history, is suggested for possible development of spontaneous tolerance”

Ara h 2 (cut off 0.44) has 82% sensitivity and 92% specificity cf 84 and 86% for SPT of 4mm, so equivalent. Cor a 14 (cut off 0.64) has 73 and 95%, so not great sensitivity. Ana o 3 (cut off 0.4) pretty good – 96 and 94%.

If random reactions, then consider hidden allergens: celery, mustard, cochineal, lupin, soy, fenugreek, other legumes such as pea/bean/lentil protein, insects/mealworm, pink peppercorns.

Panel tests

=multiple specific IgE tests done at the same time (the ultimate being the ALEX test, where 250 different antigens are tested simultaneously) – likely reduced sensitivity, compared with individual test, but more importantly, potential for false positives, with attendant harms (including iatrogenic food allergy, if that food then avoided unnecessarily).