Maloney JM, Rudengren M, Ahlstedt S, Bock SA, Sampson HA. J Allergy Clin Immunol. 2008;122(1): 145–151
PURPOSE OF THE STUDY. The authors of this study sought to determine the usefulness of peanut-, tree nut–, and seed-specific immunoglobulin E (IgE) measurements for the diagnosis of symptomatic allergies and to learn more about the relationships among these foods.
STUDY POPULATION. Children and adults (N = 324) referred to a private allergy practice and to an academic center allergy clinic for evaluation of suspected IgE-mediated peanut, tree nut, or seed (sesame seed, mustard seed, poppy seed, rapeseed, and cottonseed) hypersensitivity were enrolled in the study. Patients ranged in age from 2.4 months to 40.2 years (median: 6.1 years). The male/female ratio was 198:126. Atopic dermatitis occurred at some point in life in 57% and asthma in 58%. Many had or “outgrew” other food allergies.
METHODS. Patients answered a questionnaire about their perceived food allergies. Allergen-specific diagnoses were based on questionnaire, medical history, and, when relevant, skin-prick test results and serum-specific IgE levels. Sera were analyzed for specific IgE to peanuts, tree nuts, and seeds by ImmunoCAP (Phadia AB, Uppsala, Sweden).
RESULTS. Seventy-two percent of the patients had convincing histories of peanut allergy. Of these, 86% had sensitization to ≥1 tree nut, with 34% having clinical allergy. The majority of study patients had never ingested tree nuts, which made it difficult to determine the true prevalence of these nut allergies. Tree nut clinical allergy occurred with a frequency ranging from 16.4% for walnut to 1.5% for Brazil nut. Seventeen percent of the patients reported reactions to sesame seed. The ranges of increased serum-specific IgE levels for each food varied widely among patients with positive histories. The relationship between diagnoses and allergen-specific IgE levels was estimated through logistic regression, with curves illustrating the likelihood of receiving a positive clinical diagnosis in relation to the specific IgE concentration. Positive predictive values (95%) were established for peanut and walnut (13 and 18.5 kUA/L, respectively) but with sensitivities of just 60% and 17%, respectively. High correlations were found between IgE results for walnut and pecan and between those for cashew and pistachio.
CONCLUSIONS. Quantification of food-specific IgE is a valuable tool that can aid in the diagnosis of symptomatic food allergy and might decrease the need for double-blind, placebo-controlled, food challenges.
REVIEWERS COMMENTS. The standard method for diagnosing food allergy is the double-blind, placebo-controlled, food challenge, but the procedure is time-consuming and is not risk-free. It is well known that sensitization to foods, as defined by the presence of specific IgE, may occur in the absence of allergic reaction on ingestion (“clinical allergy”) and vice versa. Therefore, studies such as this one provide insight on the predictive value of the tests. Nonetheless, patients with serum-specific IgE levels less than the diagnostic decision points may require a physician-supervised oral challenge. It is also important to appreciate that immunoassays vary according to manufacturer, and reported results are not necessarily equivalent. Also, the severity of clinical reactions is very poorly predicted by the absolute levels measured.
- Copyright © 2009 by the American Academy of Pediatrics