More news on the diagnosis, or misdiagnosis, of peanut allergy.

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Hey! We’re back.

I took a little hiatus from the blog.  We had a really busy tree season, I moved into a new house, and we had a little rain in the Nashville area.  My thoughts have been elsewhere.

For my re-entry post I thought I’d touch on a recent article looking at the mess that is peanut allergy diagnosis.  I’ve written about this before and related the uncertainty inherent in interpreting food allergy tests- particularly food allergy blood tests.  In simplest terms, food allergy testing is very good at ruling OUT allergies, but when the test comes back positive then in doesn’t necessarily indicate a true allergy.  How do we handle this?

It may be helpful at this point to draw a distinction between sensitization and allergy.  When an allergy blood test comes back positive, that shows sensitization: the body’s immune system has come into contact with that substance and has responded to it by making a specific allergy antibody, sIgE in the medical shorthand.  The problem is that sensitization to a substance does not mean a person is allergic to that substance.  An allergic person will have a reaction when exposed to that substance, but many people who are sensitized are not allergic.

Are you more confused?  Lets look at the study to clarify.

Researchers in the U.K. and Sweden tested 933 kids and found that around 12% were sensitized to peanut (had a positive test), but only about 2.5% had true peanut allergy (reacted when they ate peanuts).  That means that 75-80% of kids with a positive peanut test weren’t peanut allergic in this study.  Imagine how many families are needlessly stressing over peanut allergy!

The study used oral peanut challenges-having the kids eat peanuts- as a gold standard for diagnosing peanut allergy.  Most community allergists don’t do this because they lack the resources to properly carry out the test.  Many families are wary of doing this because of the risk of severe reactions.  These researchers used a new test called component resolved diagnostics (CRD)to see if they could better identify who was truly allergic and who was simply sensitized.  CRD works like a usual allergy blood test except that it measures sensitization to very specific parts of the peanut protein.  The researchers found kids who were sensitized to one particular peanut component, called Ara h 2 if you need to know, were much more likely to react to peanuts.

This is only one study and I’m not sure yet how CRD will fit into clinical practice just yet.  However, I think it is very promising and I’m hopeful that it will give us a useful tool to better diagnose and manage peanut allergy.

Dr. O

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