Peanut allergy is a prominent IgE-mediated food allergy that can cause anaphylaxis and it is increasing in prevalence. Peanut allergy appears to be particularly persistent. Detection of allergen specific IgE supports the diagnosis of peanut allergy.
Peanut Component Testing, can help diagnose specific peanut allergy.
There are over 13 allergenic components identified in peanuts. The most important markers that have been identified are Ara h 1,2,3,6,8 and 9. Ara h 1, 2 and 3 are seed storage proteins and sensitization to them is associated with a high risk of a systemic allergic reaction (anaphylaxis). Ara h 2 is a more important predictor of clinical peanut allergy than Ara h 1 and 3, and is most often associated with severe allergic reactions.
Ara h 8 is associated with a low risk of systemic reactions and a moderate risk of oral allergy syndrome. Ara h 8 cross reacts with Birch pollen. Ara h 9 sensitization can result in systemic reactions, however the amount of Ara h 9 in peanuts is generally low. Ara h 9 is cross reactive to fruits with pits, i.e. peaches.
Specific-IgE to Ara h 2, a peanut protein is the best antibody test to confirm the diagnosis of peanut allergy. Ara h 6 shares multiple similarities with Ara h 2.
A recent study published looked into which peanut allergen bound to IgE more strongly and induced the greatest activation of mast cells (cells involved in allergic reactions to peanut). They found:
- Specific IgE to Ara h 2 had identical sensitivity but improved sensitivity compared to Ara h 6.
- IgE from individuals who had IgE to both allergens bound Ara h 2 more than Ara h 6.
- Ara h 2 activated a greater proportion of mast cells with a lower concentration of allergen
In clinical practice, the detection of Ara h 2 specific IgE is sufficient to diagnose most patients. However a combination of Ara h 2 and Ara h 6 in cosensitized patients may be an approach to future immunotherapy going forward.
Update November 2, 2022
A recent study published in JAMA showed that early dietary introduction has not in fact reduced peanut allergy prevalence. Infant feeding guidelines were changed in 2016 to recommend early peanut feeding before age 12 months on the basis of multiple randomized clinical trials showing reduced rates of peanut allergy with early introduction. In Australia over 7000 children were studied with these new guidelines and the rates of peanut allergy between the 2 groups did not show a significant difference (3.1% in the early vs 2.6% in later introduction). In total these results demonstrate that early dietary introduction has not yet reduced peanut allergy on a population wide level.
Despite these results, it is still recommended to introduce peanut earlier in children. It may take time for the results to show significant benefit on a population wide-level.
Caregivers are not supporting early peanut introduction guidelines