Gold standard is double blind challenge, but who has time for that?
Mostly based on history – combination of characteristic features without other, more likely, explanation.
NICE has list of type 1 vs non type 1 allergy signs/symptoms – some overlap, eg vomiting, diarrhoea, itch.
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
- For peanut, hazelnut or cashew, if in doubt do component tests Ara h 2, Cor a 14, Ana o 3 respectively as well (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)
- “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. Cor a 14 (cut off 0.64%) has 73 and 95%, Ana o 3 (cut off 0.4) 96 and 94%.
Common hidden allergens (!): celery, mustard, cochineal, lupin, soy, fenugreek, other legumes such as pea/bean/lentil protein, insects/mealworm, pink peppercorns).