Nut allergy screen (mix)

The test measures, in one go, IgE antibodies against a fixed mix of 5 foods: peanut, hazelnut, Brazil nut, almond and coconut. Botanically, peanut is not a nut but a legume, and according to Stichting Voedselallergie (Dutch food allergy foundation) coconut is a fruit; both are included in this mix. IgE is the type of antibody that, in an allergic reaction, triggers mast cells to release histamine; the body only makes these antibodies after it has previously been in contact with an allergen, and this is called sensitization. Because the 5 foods are tested together, the result gives one number and a verdict of positive or negative, but not which food the antibodies are directed against. Other nuts, such as walnut, cashew, pistachio, pecan and macadamia, and sesame are not in the mix.

• Sensitization to at least one of the 5 foods in the mix: the body has made IgE antibodies against one or more of them
• A first indication of whether an acute reaction shortly after eating may be related to peanut or one of these nuts

The GP mainly looks at the history: which food, which symptoms, how soon after eating and how often. With a positive result, separate IgE tests follow if needed to see which nut it is, or whether it is peanut. With a suspected real allergy or after a severe reaction, referral to an allergist or pediatrician follows, where a food challenge is done if needed.

A positive IgE result shows sensitization, not allergy: it only says that there are antibodies, not that you get symptoms from that food. The Dutch medical specialists' guideline (FMS) on food challenges advises against IgE tests for many foods at once and food mixes if there is no suspicion based on a good history of the symptoms, and calls a supervised food challenge the gold standard. With peanut and nuts, cross-reaction with birch pollen often gives a positive result without a real food allergy. The mix is therefore mainly a first step after a clear reaction: a negative result makes an allergy to these 5 foods less likely, a positive result calls for separate tests.

• Sensitization without symptoms is common, mainly through cross-reaction with birch pollen; the result can only be interpreted together with the history of the symptoms.
• The test does not say which food is the cause; that requires separate IgE tests.
• The test measures all proteins per food together; testing for single proteins, such as Ara h 2 in peanut, says more about the chance of a severe reaction.
• Nuts outside the mix, such as walnut, cashew, pistachio, pecan and macadamia, and sesame are not tested.

According to Stichting Voedselallergie, 1 to 2 in 100 people in the Netherlands have a nut allergy, both children and adults. Peanut allergy usually starts at a young age and often lasts a lifetime. Peanut and nuts can cause severe reactions, while sensitization without symptoms is much more common than the allergy itself.

Useful after a clear reaction shortly after eating peanut or nuts, such as itching in the mouth, hives, swelling, vomiting or shortness of breath, when it is unclear which food is the cause. If it clearly concerns one food, a separate IgE test says more. With vague symptoms without a clear link to a meal, and in people who eat peanut and nuts without problems, the test adds little; the FMS guideline then advises against screening.

• A positive result without a clear reaction can lead to unnecessarily cutting out peanut or nuts; according to Stichting Voedselallergie, cutting them out for a long time actually increases the risk of an allergy that may later be more severe.
• A negative result can give false reassurance with an allergy to a nut or seed that is not in the mix.

• NHG-Standaard Voedselovergevoeligheid en coeliakie (M47)
• FMS Richtlijnendatabase: Voedselprovocatie, module Plaatsbepaling diagnostiek voedselallergie
• NVKC, allesovertesten.nl: Allergie (RAST)
• Stichting Voedselallergie: Noten
• Stichting Voedselallergie: Pinda