Peanut Allergy Diagnosis

Source: Dang TD, Tang M, Choo S, et al Increasing the accuracy of peanut allergy diagnosis by using Ara h 2. J Allergy Clin Immunol. 2012;129(4):1056-1063; doi:10.1016/j.jaci.2012.01.056.  See AAP Grand Rounds commentary by Dr. Sai Nimmagadda (subscription required).

PICO
Question: Among infants, does Ara h 2 antigen testing accurately diagnose peanut allergy?
Question type: Diagnosis
Study design: Randomized controlled

I just finished a handful of peanuts (roasted, unsalted of course) and count myself among the lucky folks who don't have peanut allergy.  For those that might have allergy, diagnosis has long been plagued by lack of an easy, accurate means of diagnosis.  The gold standard is an oral food challenge (OFC), but this is a costly and prolonged process that carries a risk of anaphylaxis.  This study of 200 children, half with OFC-positive peanut allergy and half without, found that measurement of serum Ara h 2-specific IgE antibody was better than measurement of serum whole peanut-specific IgE antibody (sIgE).  When cutoff values were set for equal specificities of 98% for both assays, the Ara h 2 antibody was 60% sensitive (95% CI 50-70%), compared to 26% (18-36%) for the sIgE.  That's an improvement, but very far from what is needed to replace OFC.  A screening test for a serious illness needs to achieve high sensitivity, to avoid missing any cases, accepting a few more false positive results as a tradeoff.

As noted by Dr. Nimmagadda in his commentary, Ara h 2 is the predominant peanut allergen in Europe, North America, and Southeast Asia, but Ara h 9 predominates in Spain.  It's clearly not a simple problem to be solved.

On a final note, this study was performed by the HealthNuts study group in Australia.  Normally I'm a bit nonplussed with cute names for study groups, but this one seems to hit an appropriate, nice tone.