Help! My allergy test showed a positive result to a food I’ve been eating my whole life!

If an IgE allergy test showed a positive result to a food you’ve been eating your entire life without issue, and you can still eat it without any symptoms, it is likely your immune system may have become tolerant, or desensitized, to that food and you won’t experience symptoms from eating it. Tolerance is your body getting used to the allergen overtime, to where your immune system recognizes the allergen and it doesn’t have the same strong reaction as before.

However, if IgE food testing is used as a screening test, as you are not sure what you are having symptoms from, the result might be a false positive, because IgE food testing has a low positive predictive value. 

A low positive predictive value means that a positive IgE result may not be a true allergy. A “ low positive predictive value” of any test means that there can be false positives. This signifies that something showing up as a positive result, say “cashews”, may not be a true allergy. Thankfully, food allergy IgE testing has few false negatives, or what we call a high negative predictive value. This implies that if it does not show up as an allergy, it is probably not an IgE allergy.

If you get a positive result, a way to differentiate whether it is true or not is to do a food elimination challenge, whereby you remove the suspected food for several weeks and then reintroduce it and see if it incites any symptoms. If the suspected food does not cause symptoms, then it may be a false positive IgE result.

The true gold standard for diagnosis, and then management of, a true food allergy is based on an oral food challenge, and symptoms from ingesting the allergen