There are no available clinical tests that can accurately predict peanut allergy (PA) and/or anaphylaxis. This study evaluated whether the component-resolved diagnostic (CRD) IgE tests can:- distinguish PA from asymptomatic peanut sensitization (PS)
- differentiate anaphylactic from nonanaphylactic PA
Peanut allergy cases (with or without anaphylaxis) had higher IgE reactivity to Ara h 1–3 (peanut allergens) and Gly m 5–6 (soy allergens) than asymptomatically sensitized children.
IgE to Ara h 2 was the major contributor to accurate discrimination between PA and asymptomatic sensitization. With an optimal cutoff point of 0.65 ISU-E (ImmunoCAP), it conferred 99.1% sensitivity, 98.3% specificity, and a 1.2% misclassification rate in the prediction of PA, which represented a higher discriminative accuracy than IgE to whole peanut extract.
However, none of the IgE could significantly differentiate peanut anaphylaxis from nonanaphylactic PA.
IgE to Ara h 2 can efficiently differentiate clinical PA from asymptomatic PS, which may represent a major step forward in the diagnosis of PA.
It is important to note that in 10–25% of food allergy reactions, sIgE can be undetectable by blood test (http://buff.ly/1e7HAmY).
Editor's note: The study did not include a comparison with skin testing which is a much less expensive and readily available alternative. The cost of skin test with positive and negative control and peanut extract is $25 (covered by most insurances). The cost of the commercially available sIgE for Ara h2 is $300 (not covered by insurance).
8 top allergens account for 90 percent of food allergies. Specific IgE levels (sIgE) that predict the likelihood of passing an oral food challenge are shown in the figure. (click to enlarge the image).
Comparison of diagnostic methods for peanut, egg, and milk allergy - skin prick test (SPT) vs. specific IgE (sIgE) (click to see the spreadsheet). Sensitivity of blood allergy testing is 25-30% lower than that of skin testing, based on comparative studies (CCJM 2011).
References:
IgE, but not IgG4, antibodies to Ara h 2 distinguish peanut allergy from asymptomatic peanut sensitization. Hong X, Caruso D, Kumar R, Liu R, Liu X, Wang G, Pongracic JA, Wang X. Allergy. 2012 Dec;67(12):1538-46. doi: 10.1111/all.12047. Epub 2012 Oct 25.
http://www.ncbi.nlm.nih.gov/pubmed/23094689
Peanut allergy: Diagnostic accuracy of sIgE to Ara h 6 in adults is as good as Ara h 2 http://buff.ly/1uU314i
Below is a marketing video from ImmunoCAP Peanut Component test. From the test manufacturer's YouTube channel: "The mother of a patient shared the story of her son who was diagnosed with multiple food allergies as an infant. After a peanut allergy diagnosis, the family's world was turned upside down. Recently, when starting Kindergarten, his doctor recommended the ImmunoCAP Peanut Component tests and, like 75% of all peanut sensitized individuals, the test results indicated he was not clinically allergic. He can now eat peanuts without fear."