The diagnosis of
food allergy is often difficult to make by conventional means. Histories are frequently ambiguous, and skin testing is of dubious reliability because of the number of false-positive and false-negative reactions. We have evaluated the radioallergosorbent test (RAST) for the in vitro measurement of the specific
IgE antibodies to nuts, including Brazil nut, almond, walnut, pecan, cashew, and the legume, peanut. Serums were obtained from 18 patients with a history of
nut allergy and
IgE level and specific
IgE antibodies were measured. Thirteen of the 18 patients had significantly elevated
IgE antibody (greater than twice control) to one or more of the
allergens. Prausnitz-Küstner tests on selected serums in general corroborated the results of the in vitro studies. Five patients had RAST elevations to 2 or more nuts. As a group RAST-positive patients had elevated mean serum
IgE levels and more severe clinical symptoms (p less than 0.01). The specificity and cross-reactivity of
IgE antibodies to different nut
antigens was investigated by RAST inhibition with serums from 5 patients having high levels of
IgE antibody. In 4 patients no cross-reactivity between Brazil nut and peanut was found. In contrast, several nut extracts inhibited the reaction of pecan
allergen with
IgE antibodies. These results indicate that specific
IgE antibodies can be measured by RAST in patients with
nut allergy and the cross-reactivity of nut
antigens can be investigated. RAST would appear to be most useful in confirming the diagnosis of
nut hypersensitivity in children or in highly allergic patients in whom skin testing poses a risk of
anaphylaxis.