Discussion of Outgrowing Peanut Sensitivity

PEANUT ALLERGY: Peanut sensitivity is a common allergy in North America and because this allergy is often associated with anaphylactic reactions and because it is a common foodstuff, peanut sensitivity represents one of the most worrisome of allergic reactions. Anaphylaxis is defined as a multisystem allergic reaction and in children is most threatening when the reaction involves the respiratory system (any of choking, stridor, coughing, wheezing). The initial reaction to peanut is associated with respiratory symptoms in about 20% of children but later reactions are associated with respiratory symptoms in 50% or more of children. Go to Article Abstract Go to Article

A reaction to peanut is usually confirmed by a positive peanut skin test or RAST test (measurement of specific IgE antibody to peanut). Nevertheless a positive skin test and/or RAST test to peanut does not automatically mean that there will be a clinical reaction but the larger the positive skin test or the higher the RAST test value, the more likely there will be a clinical reaction if peanut is consumed. Sampson and Ho have published that a RAST IgE antibody measurement of 15 KU/L or higher indicates a 95% likelihood of a clinical reaction on oral challenge of the patient with peanut.  Go to Abstract Go to Abstract  Despite the almost certainty that a high level of IgE antibody to peanut will be associated with a clinical reaction, it is not possible to predict the severity of the reaction by either the size of the positive skin test or the quantity of IgE antibody determined by a RAST test. Moreover there does not seem to be a lower limit of IgE antibody below which it is possible to say that there will be no clinical reaction. Go to Abstract

Because of the number of children said to be allergic to children, it has become increasingly important to assess those children by an oral challenge with peanut in an appropriate hospital unit. Go to Abstract

OUTGROWING PEANUT ALLERGY: It is common for allergic children to outgrow sensitivity to milk and egg Sampson, editorial while it was considered that sensitivity to peanut is lifelong. Go to Abstract For some time, I noticed in my office practice that there were a few children who having reacted to peanut in infancy, lost the positive skin test as they got older and that could be confirmed with a RAST test that was below the level of detection (i.e. <0.35 KU/L). These children seemed to be among the least atopic. This observation was first published formally by Hourihane and Warner. The complete manuscript is available on line along with some discussion. Go to the Hourihane study The study was a case-control design in which 15 children who had a history of reaction to peanut and later underwent a negative oral challenge with peanut were compared with 15 children who had a positive oral challenge. There were some weaknesses in the study since some of the patients had not been seen by the authors at the time of the reaction to confirm that they were indeed sensitized to peanut. The results were met with some sceptecism since it had been the prevailing wisdom that children do not outgrow the sensitivity to peanut. Go to Letter. Since Hourihane et al. had not necessarily seen the patients who had resolution of their peanut sensitivity at the time of their initial reaction, it was possible to question their results.

LOSS OF POSITIVE SKIN TEST: In 1999, we began a study to evaluate continuing peanut sensitivity in patients who were referred for re-assessment having been diagnosed as peanut allergic by myself in the past. In that year we saw 96 patients for re-assessment and found that of the 96, 10 had lost the positive skin test to peanut. This was confirmed by a negative RAST result showing <0.35 KU/L and then an oral challenge was performed in the office. We confirmed that these children were generally less atopic than children who retained the positive skin test to peanut, with fewer positive skin tests to other allergens, less sensitivity to nuts, less eczema and less asthma. Go to full study

Go to Cases Illustrating Loss of Peanut Allergy

LOSS OF REACTIVITY TO PEANUT WITH A POSITIVE SKIN TEST. There are two ways a child can outgrow sensitivity to peanut. In the first instance, as described above, the child actually loses any detectable IgE antibody to peanut. However in other cases, the child maintains the positive skin test and RAST to peanut but loses clinical sensitivity. That is formally proven in the study described below. It is not known whether there is a difference in the long-term outcome of these two types of peanut sensitive children but some children do have a recurrence of their peanut sensitivity over time.

Skolnick HS, Conover-Walker MK, Koerner CB, Sampson HA, Burks W, Wood RA. The Natural History of Peanut Allergy. J Allergy Clin Immunol 2001 Feb;107(2):367-74 Go To Abstract

METHOD: 223 patients age 4 - 20 years were evaluated by questionnaire, skin testing and RAST testing, for entry into a study of oral challenge with peanut. Patients with a RAST test score of IgE antibody to peanut greater than 20 KU/L were excluded. Dr Sampson has previously published that RAST measurement of specific IgE antibody to peanut and other foods could be used to establish a concentration at which there was 95% likelihood of a clinical reaction so oral challenge did not need to be done.Of the 223 patients, 97 were excluded because of the high RAST to peanut, and 41 declined to undergo the challenge.

RESULT: Forty-eight (21.5%) patients had negative challenge results and were believed to have outgrown their peanut allergy (aged 4-17.5 years [median 6 years]; PN-IgE < 0.35-20.4 kUA/L [median 0.69 kUA/L]). Thirty-seven failed the challenge (aged 4-13 years [median 6.5 years]; RAST < 0.35-18.2 kUA/L [median 2.06 kUA/L]).

CONCLUSIONS: Peanut allergy is outgrown in about 21.5% of patients. Patients with low peanut IgE levels should be offered a peanut challenge in a medical setting to demonstrate whether they can now tolerate peanuts. While the patients with a positive challenge result had a higher RAST value than those who underwent a negative challenge, (2.06 vs 0.69) there was a lot of overlap and there were positive challenge even with a RAST <0.35 which is below the level of detection. Presumeably those patients had a positive skin test despite the undetectable serum IgE antibody to peanut. Overall, they found that PN-IgE levels were the best guide to determine which patients should be considered for a formal challenge. However, there were 6 patients with negative RAST results and 2 with both negative RAST and skin test results who had positive challenge results (1 open and 1 DBPCPC). The reactions during challenge in this group varied from limited urticaria to multisystem involvement, which emphasizes the limitations of these test methods and the importance or performing all challenges in a controlled setting.

SUMMARY: As mentioned, Sampson has published that the chances of reacting clinically to peanut is >95% when the RAST IgE level is 15KU/L or higher. It has also been shown that patients having just a skin reaction to peanut have less IgE antibody than those who have a multisystem reaction. Despite that there is no threshold level of IgE antibody below which it is possible to say that there will never be a clinical reaction. Go to Abstract As a result it is very important that all children with peanut sensitivity be equiped and instructed on the use of an EpiPen. They should practice strict avoidance. However a percentage of the children can lose sensitivity to peanut by either losing the IgE antibody to peanut or losing the clinical reactivity despite maintaining the presence of specific IgE antibody to peanut. Oral challenge with peanut in a suitable facility should be offered to selected peanut-sensitive individuals in order to identify those who have lost clinical sensitivity.