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Peanut Allergy research – Dr. Ham Pong
An Overview of Dr. Ham Pong’s Clinical Research: A comparison of prick skin test (PST) and peanut-specific IgE (p-IgE) values with oral challenges.
AAIA Newsletter 2 – 2004
The Research was presented at the XI International Food Allergy Symposium, New Orleans 2003 & American College of Allergy, Asthma & Immunology Meeting, New Orleans 2003.
Research has found the peanut allergy can resolve in up to 20% of children. Knowing which children will outgrow their peanut allergy and who should be given a peanut challenge is a constant trial for allergists. The hope of outgrowing an allergy is a constant for parents of children with life-threatening allergy and for the children themselves.
In order to further aid in assessing which allergic children would be most likely to outgrow peanut allergy, Dr. Ham Pong chose to do a study in his practice to attempt to further delineate which peanut allergic children can be safely challenged. For the study he chose 60 children aged 4 – 13 years. The children were chosen based on the following criteria:
The p-IgE was less than or equal to 5 ku/L. This is the CAP or Unicap test which assesses the IgE level of the patient suspected of peanut allergy. This was either previously diagnosed based on a history of immediate IgE type allergic reactions to peanut and a positive PST (prick skin test) OR a positive PST but the child had never ingested peanut.
The child had no allergic reactions to peanut for over 2 years.
Generally children were required to be over 5 years of age to be considered for an oral challenge, however occasionally younger children were chosen if it was felt they would be cooperative. The challenges were primarily done in an office setting with informed consent. However on occasion they were done in a hospital setting also after informed consent.
The majority of the challenges started as a single blind challenge for the first 4 doses and proceeded to open challenges when the dose of peanut equaled or exceeded one peanut. The placebo consisted of crushed nut-free chocolate candy, which the patients had tolerated in the past. Since a form of milk chocolate was used, for children with co-existing milk allergy, a different placebo was used.
A negative challenge was indicated by tolerance of a cumulative dose of 21 – 28 peanuts over a 3 hour period, with a single final dose of 12 peanuts. A challenge was considered positive if there were objective signs suggestive of an IgE mediated allergy e.g., urticaria (hives), angioedema (swelling), bronchospasm (wheezing), immediate vomiting, etc.
Positive oral challenges occurred in 17 of the 60 children, or 28% of the cases. There was 1 (one) equivocal challenge from the group of the 60 children.
Negative oral challenges occurred in 42 of the 60 children, or 70% of the cases. In this group, 31 or 74% had a positive prick skin test. As a group these children had lower prick skin tests and p-IgE than the positive challenges. On an individual basis prick skin tests and/or p-IgE did not separate those with negative or positive challenges, or anaphylaxis except for a negative prick skin test that always resulted in a negative challenge.
Of the 60 children, 28 had negative p-IgE. Six of these 28 had positive challenges. Therefore a negative p-IgE still resulted in a positive challenge in 21% of children. While a negative p-IgE often implies that the peanut allergy may be gone, it is not always so. Of the 6 children with a negative p-IgE who had reactions on challenge 3 resulted in mild anaphylaxis. These reactions were easily reversed with treatment.
Final results of the study found that Unicap testing predicated a larger number of peanut allergy resolvers than prick skin testing. In general, PST size and p-IgE were lower in the negative challenge versus the positive challenge groups. However, on an individual basis, neither were predictive of negative challenges, or anaphylactic response during a positive challenge. The only exception was a negative PST which predicted a negative challenge, irrespective of the p-IgE.
If your child has not had an allergic reaction to peanut for over 2 years, you may want to check with your allergist to see if they meet the criteria for an oral challenge. This study clearly confirms that 70% of children who have not had a reaction for over two years and who also meet the criteria for lowered p-IgE and based on prick skin testing may have out-grown their peanut allergy.
The conclusion of the study confirms that peanut allergy can resolve in some children. However, follow up of these apparent peanut resolvers is important to ensure they have truly outgrown their allergy.
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