High RAST+ for peanuts with no visible reaction??

My 2.5 year old daughter just tested positive for peanut allergies with a RAST level of >100. We only had the test run as a precaution, not because we anticipated this result (she has eczema, so we thought we were simply being prudent).

I am struggling to make sense of this, since she has had peanut butter at least 4 times in her life and nothing happened - no hives, no vomiting, no wheezing, etc. On one occasion she threw up while eating peanut butter on apple slices, but I wasn't sure if it was the peanut butter or the fact that she was having trouble with the skins I left on the apples (and has a tendency to take enormous bites without chewing).

From what I've read, a Level 6 RAST test correlates with a 100% chance of a reaction. Moreover, the allergist we met with today said that, based upon my daughter's IgE, we could expect any reaction to be severe. Please, please clarify this apparent discrepancy between test and history for me.

[Bhupinder Kaur, MD]

Hello,

RAST  is one of the confirmatory tests for testing allergies but false results are sometimes present when it is used for food allergy testing.You are saying that your daughter has eczema. Many patients with eczema have very high levels of total IgE. False positive results may be seen in these cases. This is because there is so much IgE present in the blood sample that it shows up as a positive result for foods that the person is not allergic to. Similarly, foods with similar protein structures may cross-react, resulting in false positive results.But the only point is false positive results mostly show at low level positive.High level positive generally means that the person is allergic to that allergen.

I feel that you should discuss this with her allergist and get food challenge tests done to see if she really is allergic to peanuts.

I hope it helps.Take care an pls do keep me posted. Kind regards