Measurement of whole peanut-specific IgE (sIgE) is often used to confirm sensitization but does not reliably predict allergy. Ara h 2 is the dominant peanut allergen detected in 90% to 100% of patients with peanut allergy. Ara h 2 IgE could help improve diagnosis of peanut allergy.
This study from Australia included 200 infants from the population-based HealthNuts study who underwent:
- skin prick tests to determine peanut sensitization
- a peanut oral food challenge (OFC) to confirm allergy status
By using the previously published 95% positive predictive value of 15 kU(A)/L for whole peanut sIgE, a corresponding specificity of 98% was found in this study.
At the equivalent specificity of 98%, the sensitivity of Ara h 2 sIgE is 60%, correctly identifying 60% of subjects with true peanut allergy. This is compared with only 26% correctly identified by using whole peanut sIgE.
When using a combined approach of sIgE testing for whole peanut followed by Ara h 2 for the diagnosis of peanut allergy, the number of oral food challenges (OFC) required was reduced by almost two thirds.
The authors concluded that Ara h 2 plasma sIgE test levels provide higher diagnostic accuracy than whole peanut plasma sIgE levels. It is a new diagnostic tool to distinguish peanut allergy from peanut tolerance, which might reduce the need for an oral food challenge (OFC).
Editor's note: The test costs $300 in the U.S. and is not covered by most health insurances (uKnow Peanut from Phadia http://bit.ly/OJjRyI).
Molecular Allergy Component Testing, a video by the manufacturer of ImmunoCAP testing system.
This video by the manufacturer of sIgE assays Phadia tries to explain the concept of Molecular Allergology in two minutes:
Increasing the accuracy of peanut allergy diagnosis by using Ara h 2. Dang TD, Tang M, Choo S, Licciardi PV, Koplin JJ, Martin PE, Tan T, Gurrin LC, Ponsonby AL, Tey D, Robinson M, Dharmage SC, Allen KJ; HealthNuts study. J Allergy Clin Immunol. 2012 Feb 29. [Epub ahead of print]
Image source: Roasted peanuts as snack food, Wikipedia, public domain.