An important question for researchers and clinicians who work with food allergies is whether food-specific IgE and skin prick test results can be used reliably as ersatz measures of allergen sensitization (see also our News Beyond Our Pages blog from May 14). The reason is that the clinical standard for food allergy diagnoses is double-blind, placebo-controlled food challenge, which is expensive, costly, and requires dedicated personnel and facilities because of the risk of anaphylaxis.
In a Letter to the Editor in JACI (J Allergy Clin Immunol 2010;125:1391-2), van Nieuwaal et al. report results from a study conducted in 103 children with suspected peanut allergy. Peanut-specific IgE levels were correlated to results of diagnostic food challenge to evaluate the predictive power of specific IgE and food challenges were performed regardless of a possible history of anaphylaxis. The population was very atopic as well, with greater than 80% having atopic dermatitis. The authors report that peanut-specific IgE was correlated to positive food challenge results in approximately 55% of the children. Specificity of IgE values of 10.4 [92%], 24.8 [98%] and 25.5 kU/L [100%] were significant for predicting outcome of food challenge. The authors note that the specific IgE levels were not sensitive, though, and that values lower than these do not indicate that there would be no reaction to oral food challenge.
The authors conclude that using these IgE levels as cutoffs would obviate diagnostic oral food challenges in at least some of the children. Oral food challenge would still be needed to determine the sensitivity and severity of the peanut allergy.
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I'm wondering how IgE results compare with skin prick test results. In 2008 my daughter's SPT was 8x11mm, and her IgE was 69. In 2011, her SPT was 3x7mm, but her IgE had elevated to over 100. Does this mean she is more severely allergic now?
ReplyDeleteMelissa,
ReplyDeleteThank you for your question. We can't speak to your daughter's specific situation -- you'll have to ask your allergist about what these results mean for her. For some background information, if you haven't already read them, you might want to take a look at the relevant sections of last year's food allergy guidelines, sponsored by the National Institute of Allergy and Infectious Diseases. The full guidelines, a shortened clinicians' version, and a recently released summary version for patients, families, and caregivers, can all be accessed from www.niaid.nih.gov/topics/foodallergy/clinical/Pages/default.aspx.