Ara h2-Sige Testing Best For Pinpointing Allergy Prior To Peanut Introduction

In infants at high risk for peanut allergy, measuring the peanut component protein Ara h2-sIgE is the best way to assess whether an infant is allergic prior to introducing peanuts into the diet, researchers say.

"Previous research has shown that early introduction of peanut helps prevent peanut allergy, but whether to test some infants prior to peanut introduction is controversial," Dr. Corinne Keet of Johns Hopkins School of Medicine in Baltimore.

The team's study of potentially at-risk infants revealed a high rate of peanut allergy among those with moderate-to-severe eczema (18%) - a rate that increased with eczema severity and with increased age, Dr. Keet noted. It also found very low rates of peanut allergy among those whose only risk factor was having a sibling or parent with peanut allergy (1%).

Notably, she added, "Testing for IgE to Ara h 2 was best for telling who was peanut allergic and who was not."

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As reported in the Journal of Allergy and Clinical Immunology, Dr. Keet and colleagues enrolled 321 infants (median age, 7.2 months; 58% males; 74% white) with no history of peanut ingestion, testing or reaction but with moderate or severe eczema, a history of food allergy, or a first-degree relative with peanut allergy.

Participants received a peanut skin prick test (SPT); a blood draw for peanut-specific IgE and component-IgE testing; and, depending on the SPT wheal size, they also underwent an oral food challenge or observed feeding.

Thirty-seven infants (11%) had a peanut allergy.

Overall, Ara h 2-sIgE at a cutoff point of 0.1 kUa/L discriminated best between allergic and nonallergic children (AUC, 0.96; sensitivity, 94%; specificity, 98%).

Comparators were peanut-sIgE at 0.1 kUa/L (AUC, 0.89; sensitivity, 100%; specificity, 78%) or 0.35 kUa/L (AUC, 0.91; sensitivity, 97%; specificity, 86%) or SPT at wheal size 3 mm (AUC, 0.90; sensitivity, 92%; specificity, 88%) or 8 mm (AUC, 0.87; sensitivity, 73%; specificity, 99%).

The authors note, "Although peanut-sIgE was more diagnostically sensitive, its low specificity means that over the range of prevalences of peanut allergy expected in a screening population, most patients testing positive are not actually allergic. This results in up to one-fifth of all screened patients being misclassified as peanut allergic if a cutoff point of 0.1 kUa/L is used."

Additional analyses found that when included in a model with Ara h 2-sIgE, Ara h 1-sIgE and Ara h 3-sIgE did not add to peanut allergy prediction, whereas Ara h 8-sIgE discriminated poorly (AUC, 0.51).

Dr. Keet said guidelines will be affected in the following ways:

- More support for recommending very early introduction of peanut products in high-risk children (at ages 4-6 months) and for screening some infants (particularly those with severe eczema) prior to introduction

- Siblings of peanut allergic children do not need screening tests prior to peanut introduction if they themselves do not have bad eczema

- Screening only with the IgE to Ara h 2, instead of IgE to peanut or skin prick tests.

"Currently, it is usually not possible, but we hope that labs will allow for providers to order IgE to Ara h 2 alone," she noted.

Further, she added, "The fact that the rate of peanut allergy was already so high in the first year of life suggests that we may need to find other ways to prevent peanut allergy in addition to early introduction."

Dr. Ruchi Gupta, Director, Institute for Public Health and Medicine - Center for Food Allergy and Asthma at Northwestern University Feinberg School of Medicine in Chicago, commented in an email to Reuters Health, "We need to educate clinicians around ordering the Ara h2- peanut specific IgE and make sure it is also available for general pediatricians when they see infants at high risk for peanut allergy.

"Current recommendations are for pediatricians to order a peanut-specific IgE for high-risk infants with severe eczema or refer them to an allergist for a skin prick test and possible oral food challenge, affirmed Dr. Gupta, who was not involved in the study.

"If possible," she said, "adding the Ara h2- peanut specific IgE...for initial evaluation would be ideal to allow more high-risk infants to start peanut products without delay."

—Marilynn Larkin

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