Peanut allergy

See also Prevention, pregnancy, EAT/LEAP studies and immunotherapy.

One of the most common food allergies, and a frequent cause of anaphylaxis.  Peanut is technically a legume, although there is cross-reactivity with tree nuts so often included when people talk about “nuts”.  Always consider if there are potentially other allergies to lentils, sesame, tree nuts eg cashew etc.

Also known as groundnut or monkey nut.

[Gary Stiefel, Leicester Royal, BSACI guideline peanut allergy]

Diagnosis

Wide range of potential peanut proteins.  In US study, vast majority were Ara h1/2 positive, but European more diverse. h1, h2, h3 most common for systemic reactions.  You would think testing with whole peanut would be more sensitive but component testing probably more sensitive and specific than total IgE – but not better than skin prick testing.

peanut allergy diagnosis BSACI 2017With a decent history, SPT >3mm or IgE >0.35 sufficient.

Before proceeding to a hospital challenge, footnote suggests either 2 negatives, or else both IgE and SPT negative.

Distinguish Pollen Food Syndrome – ie older, rhinitis, oral allergy symptoms with nuts/fruit. These kids will have a milder allergy.  Hazelnut mostly (Cor a1) but almond, walnut too. But can coexist with more severe allergy! Doing grass/birch pollen would support diagnosis, doing components might help assess prognosis. If history unclear, but positive IgE/Skin prick test then do components h2 and h8 (list of different cut offs for different commercial products given, with related specificity/sensitivity, just says positive/negative in flow chart). Footnote suggests adding Ara h 1, 3 and 9 as also suggest primary peanut allergy even if Ara h 2 neg.

Sibling risk 5-9%. Too low to justify routinely screening.  If family likely to just avoid forever, living in fear, then consider SPT to encourage home challenge!?

Prognosis

Up to 20% will outgrow. Review may not be necessary if PFS only.  Follow up is essentially about education.  Testing can be done periodically, depending on resources.

In a study of adults coming to allergy clinics, 10% of peanut allergic turned out not to be.  Partly this would have been because the diagnosis was wrong (many had never actually reacted to peanut in the past).  Having eczema meant you were more likely to still be positive on testing.  Having asthma and being male made it half as likely you would not be allergic anymore.  But many of the cases described were not formally challenged so these results are of limited value.  [Poster at AAI 2021, Rima Rachid]

Avoidance

Difficult, as often used in biscuits, chocolate, ethnic foods eg satay.

As for any food allergy:

Peanut needs to be specified on food labels under UK/EU law.

Precautionary labels – impossible to eliminate risk. Often these “may contain” warnings and similar just say “nuts” without specifying whether the risk is from peanut or a tree nut (the company may be able to give further information if you enquire directly). 

Snack foods with precautionary labels are higher risk eg biscuits, cakes [Helen Brough].

Balance between convenience and risk (probably a very small risk, as many families ignore these warnings to some degree).  Stratify risk according to type of food, previous reactions, threshold, asthma, illness, time of day, location etc. Crossing the road metaphor – choose a safe place!

Should you avoid all nuts?  Some kids will be allergic to other (tree) nuts, but not all.  Andrew Clark reports v low rate of accidental reactions, 3%, with avoidance of all nuts. But increases quality of life to be allowed other nuts!  Risk assessment for each individual person!

Peanut oil

Probability of any reaction to refined peanut oil is remote (Blom et al, 2017). Little evidence that anyone has ever reacted to refined peanut oil. Code of practice is that presence of UNREFINED peanut oil should be declared on bottles of oil (UK and Europe).

But peanut oil, even if refined, still has to be declared on food labels.  Beware unrefined oil in ethnic foods.  Peanut oil also found in some medicines eg vitamins, antibiotic creams.

Some suspicion that peanut oil in cosmetics and pharmaceuticals might lead to sensitization and subsequent peanut allergy, even if not enough peanut protein to cause a reaction in an allergic person. So advice is avoid if you have a strong family history of allergy.

Immunotherapy

See Peanut immunotherapy.

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