Measurement of IgE to Ara h 2 & diagnostics for peanut allergy
Published online: January 19, 2021
Current guidelines in the U.S. recommend screening high risk infants (those with severe eczema or egg allergy) prior to introduction of peanut. Performance of this screening program has been controversial because widely available peanut specific IgE and skin prick tests have low specificity and thus there is potential for large numbers of false positives. This is particularly a problem when these tests are performed in populations with a low probability of peanut allergy, such as when screening patients who have not yet shown symptoms of peanut allergy. Component-resolved diagnostics involving specific IgE measurements to peanut component proteins may be more a specific alternative, but there is limited prospective data on how these diagnostic tests compare when evaluating infants.
In a recent article in The Journal of Allergy and Clinical Immunology (JACI), Keet et al. describe the results of a prospective study of infants at high risk for peanut allergy. They enrolled 325 4-11 month old infants at Johns Hopkins School of Medicine and Massachusetts General Hospital for Children. Inclusion criteria required moderate to severe eczema, a non-peanut food allergy, or an immediate family member with peanut allergy, but no previous introduction of peanut or testing for peanut allergy. Infants were given a peanut skin prick test and blood was drawn for measurement of peanut-specific IgE and IgE specific for the peanut-component proteins Ara h 1, Ara h 2, Ara h 3 and Ara h 8. Depending on the results of the peanut skin prick test, an oral food challenge or observed peanut feeding was performed. Predictive performance of these diagnostic tests for clinical peanut allergy was directly compared.
The authors reported that specific IgE to Ara h 2 using a cut-point of 0.1kUa/L performed the best of all the diagnostic tests, with a 94% diagnostic sensitivity and 98% specificity for peanut allergy. In contrast peanut-specific IgE at 0.1 kUa/L and peanut SPT at 3 mm wheal size had markedly lower specificity (78% and 88%, respectively), with relatively high sensitivity (peanut specific IgE 100%, SPT 92%). Measuring specific IgE to other peanut components (Ara h 1, Ara h 3 and Ara h 8) did not provide useful information. Based on these diagnostic test characteristics, the authors estimated that when used in a group of infants with a high risk of peanut allergy (20%), only 3% of patients would have a false positive or negative test result after measuring IgE to Ara h 2, compared to 18% with peanut specific IgE analysis and 11% with skin prick testing. Among low risk populations (i.e., prevalence of peanut allergy ~ 2%), the comparison is even more dramatic, with misclassifications occurring in 22% of those tested with peanut specific IgE, and 12% of those with peanut SPT as compared to only 2% with Ara h 2 specific IgE.
These findings suggest that if screening of any high-risk groups is performed prior to peanut introduction in infancy, a strategy of measuring only specific IgE to Ara h 2 would result in the fewest false positives, while maintaining a low rate of false negatives. Further, these results suggest decoupling the measurement of IgE to peanut components (Ara h 1, Ara h 3, Ara h 8) from IgE to Ara h 2 analysis. With appropriate education, this screening strategy could be performed by non-specialists, ensuring minimal delay for introduction of peanut in high-risk infants.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.
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