One of the tree nuts. One of the most common food allergens in the UK. Adults seem to get less severe reactions than children. Anaphylaxis rare compared with peanut and other tree nuts.
Hazel tree is related to birch, and indeed hazelnut allergy can be associated with tree pollen allergy (hay fever), as well as fruit allergies.
Cor a 1 is the least likely to cause systemic reactions, and then only with raw cf roast. But pretty much everyone tests positive for it, so not v helpful unless it is the only thing that is positive. You are usually also positive for rBet v 1/2, the birch pollen antigens. Cor a 8/9/14 associated with systemic, although 8 is LTP so may only be local (and likely fruit allergy too) – probably seen more often in Mediterranean populations. The others are storage proteins so more likely to cause severe reactions.
Cor a 9 and 14 seem most useful – >1kU/l and/or >5 respectively give specificity of >90% and sensitivity of 83% in kids for “allergy with objective symptoms” viz more than just a tingle/itch, so more likely to have severe reactions. That translates to a negative predictive value of about 93% (PPV not given). [Dutch study, JACI 2013;132(2):393]
German study found Cor a 14 had best AUC (0.89, cf 0.71 for whole hz). Level of 0.35 gave 85% sensitivity with 81% specificity. PPV doesn’t hit 90% until 47.8 though…