Thank you for your inquiry.
Clearly, allergy skin test reactivity to foods can change. Three years between testing is certainly a sufficient time to allow for such a change. Quite often, if there is known allergy to peanuts, patients are told to avoid peanuts and tree nuts, and vice versa. So, the strategy proposed by his previous allergist is not unusual.
Your evaluation adds another dimension to his case, and I would approach your patient as if this was the “first evaluation,” in a de novo manner. Clearly, an 8 mm wheal with a 25 mm flare implies a strong statistical chance that he would react upon the ingestion of peanuts. Since we have excellent predictive values for such reactions using ImmunoCAP, you will be able to further refine the probability of such a reaction. But at this point in time, based upon the skin test reaction to peanuts, I would certainly suggest avoidance. When the CAP-RAST returns, if this strategy is confirmed as valid (and I imagine it will), then peanut avoidance is clearly indicated.
Whether or not to avoid tree nuts is another issue. Since he has a probability of reacting to cashew, and since pistachio and cashew are related, my advice would be to clearly advise avoidance of these two nuts. And, as I mentioned earlier, quite frequently allergists suggest, in a peanut-allergic patient, avoidance of all tree nuts because of the possibility of contamination and confusion, especially in younger patients. So, I see nothing wrong with advising the avoidance of peanuts and tree nuts. But if you do not wish to have him avoid tree nuts with the lack of detection of specific IgE on skin testing, you could only make a definitive decision after oral challenge.
Therefore, in summary, my advice would be:
1. Have him avoid peanut for now. If ImmunoCAP confirms sensitivity, I would have him to continue to avoid at this time and for the immediate future. You could repeat his test annually or in a few years to see if this changes.
2. My own personal practice in this regard, especially in view of the fact that he probably had a reaction to cashew, would clearly be for him to avoid pistachio and cashew. In addition, I oftentimes advise the avoidance of all nuts.
3. If one did not want to ask this patient to avoid all nuts, the only definitive way to assure that the ingestion of nuts would be safe is to perform an oral challenge. I personally would not do so in his case, but the decision to do so is debatable, and other allergists might proceed with a challenge under these circumstances.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.