PURPOSE OF THE STUDY.
The diagnosis of food allergy can be difficult, and our current tools, including skin and serum-specific immunoglobulin E (IgE) testing, are both limited by their poor positive predictive accuracy. Oral food challenges remain the gold standard for diagnosis, but these carry risk and are time-consuming. Recently, a specific IgE measurement for individual peanut proteins (component-resolved diagnostics [CRD]) has been recognized as an additional tool for the diagnosis of peanut allergy.
A total of 205 Danish patients with a clinical history of peanut allergy (with reactions described as mild to severe) were studied, including 175 positive and 30 negative oral peanut challenges. The mean age was 5.6 years (range: 1–26 years), and the male:female ratio was 1.7:1.
Children ≤3 years old underwent open food challenge (n = 165), and those older than 3 years (n = 40) underwent double-blind, placebo-controlled food challenges to peanut. Symptom severity was classified into 5 groups. Sensitization to peanut was determined by using skin prick testing and ImmunoCAP (Phadia, Inc, Uppsala, Sweden) specific IgE testing to whole peanut (fl3) and peanut components (Ara h 1–3, Ara h 8, and Ara h 9). Challenge outcomes were retrospectively correlated with levels of specific IgE to peanut and peanut components.
Mean IgE levels for whole peanut and the components Ara h 1, Ara h 2, and Ara h 3 were significantly higher for positive challenges compared with negative challenges. The strongest correlation between clinical reactivity and specific IgE level was found for Ara h 2, for which a cutoff of >1.63 kU/L resulted in a specificity of 1.00 and a sensitivity of 0.70 in predicting oral food challenge results. Optimal cutoff points for predicting positive versus negative challenges were 2.6 kU/L for whole peanut (specificity: 0.80; sensitivity: 0.76) and 1.28 kU/L for Ara h 2 (specificity: 0.97; sensitivity: 0.76). Increasing symptom scores were correlated with higher levels of IgE to whole peanut and the peanut components Ara h 1, Ara h 2, and Ara h 3.
IgE levels to whole peanut as well as peanut components, especially Ara h 2, can help determine likelihood of reactivity to peanut. In this population, IgE to Ara h 2 would have reduced from 205 to 92 the number of oral challenges needed to clarify diagnosis. Unfortunately, however, the Ara h 2 IgE level that was found to be the most useful cutoff point in this study was higher than that found in other studies, suggesting that decision points need to be addressed in relation to specific populations. In the end, CRD may help to reduce the need for oral food challenges in some patients, but decision points may be population specific.
Although CRD testing cannot replace oral food challenges, it may be a useful tool for deciding on the appropriateness of challenge to peanut in select cases. Results of this study demonstrated significantly higher levels of Ara h 2 at decision points than previously published. These findings underscore the need for additional research among different patient groups before applying published cutoff points, given likely population-specific variations in interpretation of IgE results.
- Copyright © 2013 by the American Academy of Pediatrics