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Ask The Expert

October 21, 2013

Peanuts and Anaphylaxis Due to Cashew Nut

Question:

Recently I saw a one year-old child with a history of well-controlled eczema with anaphylaxis to cashew nut. His SPT was 13 mm wheal to pistachio (cashew was unavailable) and his specific IgE was 7.44 to both cashew and pistachio. He has never been introduced to peanut. His SPT to peanut was 4 mm (PC Histamine was 9 mm). His specific IgE is unavailable but ordered. His mother is wondering if it is safe to feed peanut butter with his history especially without prior exposure. My current recommendation was to definitely avoid all tree nuts (here is another twist – he can tolerate almond milk) and peanuts due to the potential of developing reactivity to peanuts; however, I also read that he most likely will be able tolerate peanuts.

Response

Despite the lack of cashew SPT result, the child’s high specific IgE to both cashew and pistachio in the context of an objective acute allergic reaction to cashew strongly supports the diagnosis of confirmed cashew allergy and probably pistachio allergy. Cashew and pistachio allergies commonly co-associate clinically.

There are some allergists who do not undertake screening to other nuts that have not been ingested because of the high false positive rate. However, in the context of a patient with a history of confirmed cashew anaphylaxis it in not unreasonable to undertake screening for peanut and other tree nuts since approximately 25% of those with an allergy to peanut are also allergic to tree nuts (Marco Ho et al JACI 2008).

In this context it might be worth considering doing an Arah2 serum test (component resolved diagnostics) since the test has high specificity and sensitivity for peanut allergy (Thanh Dang et al JACI 2013).

In the context of a positive screening test (although it is below the 95% PPV for peanut in this age group – Rachel Peters et al JACI 2013) I would recommend undertaking a supervised food challenge in a hospital setting rather than via home introduction.

In our department we allow patients to carefully home introduce any tree nut for which they reliably have a negative SPT provided they can be sure that the nut product is not contaminated with any of the nuts they are allergic to. However, many patients prefer to choose to avoid all tree nuts and peanuts if they have several confirmed nut allergies because it is difficult to be sure products are not contaminated with other nuts and because it can be confusing to specify which nut they can tolerate. It is important to discuss the lifestyle needs of the patient and family in this context.

There is reasonable chance the child can tolerate peanuts. If the family wishes to avoid tree nuts alone and would be willing to feed the child peanuts should he prove to be tolerant I would recommend a hospital-based challenge to confirm or refute a peanut allergy.  

Katrina Allen, MD, PhD
Department of Allergy and Immunology
Royal Children's Hospital – Melbourne, Australia


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