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 and pollen food syndrome), 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. Cor a 8 is LTP so likely fruit allergy too.

Cor a 9 and 14 (11s globulin and 2s albumin respectively, ie heat stable seed storage proteins) seem most useful  for defining kids at risk of systemic reactions – >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…