Cross-reactivity between nuts
Although clinical cross-reactivity between nuts may be difficult to establish, the possibility of exhibiting symptoms of food allergy to multiple nuts plays an important role in the management of patients allergic to nut, especially for children who are of an age where identification of individual nuts is incomprehensible. The summary of nut cross-reactivity is given in Table 1. It is common to find positive testing (skin prick or serum-specific IgE) to other legumes in those patients with history of clinical reaction to peanut. A study of 62 children with legume allergy found 79% of patients with serologic evidence of IgE binding to at least one additional legume and 37% had IgE binding to all six legumes tested, including peanut, soybean, lima bean, pea, garbanzo bean, and green beans.41,42 Despite this common finding of cross-sensitization, the rate of clinical allergy to multiple legumes is much lower. This has been demonstrated in multiple studies of children with peanut allergy, in which double-blind, placebo-controlled OFCs were used to assess clinical reactivity to soy.43,44 Although a good proportion (up to 31%) of patients allergic to peanut exhibited a positive skin test result to soy, significantly fewer children had clinical reactivity to both legumes (only 1%–3%). Another study of children with atopic dermatitis showed no reaction to any other legumes tested in children sensitive (skin test positive) to peanut.43
Co-sensitization between peanut and tree nuts is common; however only one-third of patients with peanut allergy also exhibit clinical allergy to one or more tree nuts.31 For example, one study in the UK found 59% of peanut-sensitized patients were also sensitized to hazelnut, Brazil nut, or both.45 Other studies have found limited serologic cross-reactivity between peanut and tree nuts.46 For patients with an allergy to peanut, it is important to consider age, risk of cross-contamination, and implications of dietary restrictions before recommending a peanut versus completely nut-free diet.
Similarly, patients allergic to tree nut frequently exhibit sensitization to other tree nuts. In particular, associations between certain nuts, for example, cashew–pistachio and walnut–pecan, are particularly strong. Clinical cross-reactivity to multiple nuts has been reported in up to one-third of patients evaluated for tree nut allergy.47,48 In general, only foods that have elicited reactions should be avoided, and in tree-nut-allergic individuals, previously tolerated individual tree nuts that were negative in skin test can likely be continued. In special circumstances, such as for young children, it is not uncommon to suggest avoidance of all tree nuts as to avoid accidental exposure. Individual tree nuts that have not yet been introduced can be done so by OFC in the office, if necessary. Again, this decision should be made based on clinical history, risk of cross-contamination, age of the patient, and test results.