Published Online: October 11, 2013
Evaluating the IgE response to specific proteins in peanut, component testing, is a subject of major interest in the search for an improved diagnostic test for peanut allergy. In a previous study, Klemans and Otte et al showed, in agreement with other studies in pediatric populations, that specific IgE (sIgE) to Ara h 2 is highly predictive for peanut allergy. In adults however, the diagnostic value of peanut components was not yet studied.
In a recent article published in The Journal of Allergy and Clinical Immunology: In Practice, Klemans and Broekman et al. analyzed the role of sIgE to peanut components Ara h 1, 2, 3, 8, and 9 in the diagnosis of peanut allergy in adults, and also evaluated a possible relationship with clinical severity. Ninety-four patients, 55 with a positive and 39 with a negative oral food challenge to peanut, participated. For severity analyses, 38 patients with a positive challenge from previous studies were added to the 55 patients with a positive challenge. Clinical severity was scored using several scoring systems.
The authors found that sIgE to Ara h 2 had the best diagnostic value of all peanut components . sIgE to Ara h 2 also performed better than skin prick test size and sIgE to peanut extract, which are the current standards, but this difference was not statistically significant. The positive predictive value (PPV) of sIgE to Ara h 2 when using the clinically used cut-off value of ≥0.35 kU/L was 86%, with a corresponding negative predictive value (NPV) of only 57%. This means that patients with a sIgE level to Ara h 2 ≥0.35 kU/L are very likely to have peanut allergy. A 100% PPV could be calculated when using a cut-off value of ≥1.75 kU/L. Twenty-eight percent of the studied population had sIgE above this value and could therefore be diagnosed as peanut allergic with 100% certainty. Nevertheless, caution is needed for in patients with low sIgE values to Ara h 2, since many of these patients were peanut allergic as well. This indicates that Ara h 2 cannot accurately exclude peanut allergy. All other diagnostic tests however performed even worse in excluding peanut allergy. sIgE to Ara h 2 was the only diagnostic test that significantly correlated with severity. Higher sIgE values were correlated with a more severe reaction. However, this correlation could not be translated to a useful discrimination between mild and severe allergy in individual patients.
In summary, the study showed that sIgE to Ara h 2 can accurately diagnose peanut allergy in adults, in 28% even with 100% certainty. A similar finding was previously observed in children. In addition, Ara h 2 is positively correlated to severity. It cannot however accurately exclude peanut allergy or discriminate between mild and severe allergy in individual patients. This implies that patients with negative or low sIgE to Ara h 2 can still be (sometimes severely) peanut allergic.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.