Peanut Allergy: Testing Update

June 29, 2010

Peanut allergy is generally confirmed through allergy skin testing and/or blood testing looking for peanut specific IgE.  Usually someone suspects that they or their child is allergic to peanuts because of specific symptoms that have occurred with exposure, and testing is done to confirm the diagnosis.  

There are situations however, where a child is tested for peanut allergy with either a skin test or a blood test because they have other food allergies and the parent is concerned about the possibility of also having peanut allergy.  Often this occurs before the child has ever eaten peanuts.  If this kind of testing comes back positive, it means that the child is making allergen antibody (IgE) against peanut, but it does not necessarily mean that the child will have clinical symptoms upon exposure.  

A recent study has provided some insight into what percentage of children with positive testing and no history of an allergic reaction to peanuts, actually have clinical allergy to peanuts.  The study did allergy testing in a cohort of children followed from birth.  The study found that 11.8% of children in the cohort had positive testing for peanut allergy.  An extensive analysis of the children with positive testing, including further testing and oral challenges, revealed that 22.4% of those with positive testing and no history of  having a reaction to peanuts, actually had clinical peanut allergy.  So, from this study, we can expect that about 1/4 of children who test positive to peanuts before ever consuming peanuts, will have true clinical peanut allergy.    A supervised challenge in a doctor’s office would need to be done in order to determine if a child is really clinically allergic.  Not all children are candidates for a challenge however.  This would be determined by the allergist based upon an evaluation of the skin or blood test results.  Depending on the level of positivity of the results, some children would not be considered for a challenge.

Peanuts consist of several different allergens.  The testing that is usually done commercially looks at peanut specific IgE, but does not test for each specific peanut allergen.  The study mentioned above looked at each separate peanut allergen and tried to correlate specific peanut allergens with clinical peanut allergy.  The study found that those children with positive testing to the peanut allergen called Ara h 2 were most likely to have clinical allergy.  Less than 10% of children with positive peanut specific IgE on general blood testing who could consume peanuts without having a reaction, had positive antibody testing to Ara h 2.  These results do need to be confirmed, but they are extremely interesting in that they point toward more specific testing for allergens yielding more specific answers with regard to the clinical relevance of a positive test.

Note: The content of this blog is for informational purposes only and is not meant as specific medical advice for a specific person.   If you have a medical problem, please contact your doctor.

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One Response to “Peanut Allergy: Testing Update”

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