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A new test for patients with peanut allergy

A new test is now available that can help tell us which patients are at risk for severe peanut allergy.  Results from this test may help allergists “undiagnose” some children’s peanut allergies.

The current methods of peanut allergy testing (both skin and blood tests) detect allergic antibodies to whole peanuts.  The reality is that peanuts contain 10 or more allergenic proteins.  Patients can be allergic to some peanut proteins but not others.  Also, certain peanut proteins cause worse allergies than others.  For example, peanut protein #2 is associated with more severe peanut reactions, while protein #8 is associated with mild reactions, or no reactions at all.

A new peanut “component test” can measure individual peanut proteins.  If a patient has a high total peanut level, and most of it is component #2, then the patient is more likely to have a serious peanut allergy.  If a patient has a high total peanut level, but most of it is component #8, then there is a much lower chance they will have a serious reaction to peanut.  There is a good chance they may not be allergic to peanuts at all.

How can patients have a high component #8 level, but not be allergic to peanuts?  It turns out that component #8 resembles the proteins in birch tree pollen.  So if a patient has birch pollen allergies in the spring, then there is a good chance they will also have a positive peanut test.  If you checked the peanut components, they would mostly likely have an elevated #8 level, and a low #2 level.

Why is this important?  There are patients who have been diagnosed with a “peanut allergy” who are not actually allergic.  Many children are diagnosed with a peanut allergy based on a positive test, even though they have never eaten peanuts, or even had a reaction.  Peanut component testing can help us sort out which children are at higher risk for serious allergic reactions, and which children may not be allergic at all.

If a patient has peanut component testing and is at low risk for peanut allergy, then we could talk about an oral food challenge (OFC).  During an OFC, a patient is brought into an allergist’s office and eats a tiny amount of peanut in a controlled environment.  Then the patient is monitored extremely closely for a reaction.  If there is no reaction, then the patient gradually eats larger and larger amounts of peanut.  The largest amount is usually a small handful of peanuts (or a couple tablespoons of peanut butter).

Experts consider an OFC to be the “gold standard” for diagnosing a food allergy.  If the patient doesn’t have a reaction, then this is excellent news:  they are not allergic.  However if there is a reaction (including a serious reaction like anaphylaxis), the patient is given appropriate medicines, the challenge stops, and we know that the patient is truly allergic.

Currently, only one company (PiRL, Phadia immunology Reference Laboratory) offers peanut component testing.  The test is called the uKnow Peanut Test and costs $300.  The test is still considered experimental by most insurance companies, so families must pay out of pocket.  So far, families have had little success in getting insurance companies to reimburse the cost.  We hope peanut component testing will be covered by insurance in the near future.

 

Let’s look at some real-word examples.

Example #1

Sarah is a 4-year-old girl who first reacted to peanut when she was 6 months old.  Her mother gave her a cracker with peanut butter, and Sarah reacted with red, itchy hives over most of her body.  At the time, Sarah had both skin and blood tests that were positive to peanut.  She strictly avoids all nuts (peanuts and tree nuts) and has an EpiPen Jr. with her at all times.  Sarah does not have any other allergies.  Recently her parents requested peanut component testing to verify that she is still allergic to peanuts.  Sarah had several high levels, including a high level to component #2.   Her allergist confirmed that Sarah has a peanut allergy, and advised her parents that an oral food challenge would not be useful or safe.  Sarah is still allergic to peanuts, and should continue to avoid them.  It might be worth retesting in a few years to see if Sarah has outgrown the allergy.

Example #2

Noah is a 5-year-old boy who was diagnosed with peanut allergy when he was 2 years old.  At the time he had a lot of eczema, so his primary care provider ordered a blood test looking for allergies.  The test was positive to peanuts and to cats.  Even though Noah had never eaten peanuts before, he was diagnosed with a “severe peanut allergy”.  Next year Noah will enter kindergarten, and his parents are concerned about what it means to have a peanut allergy at school:  strictly avoiding all nuts (peanuts and tree nuts), having an EpiPen Jr. available at all times, and maybe even sitting in a separate area during lunch.  His parents requested peanut component testing to verify that he is allergic to peanuts.  They also mentioned that Noah has had bad runny nose and watery eyes during the spring tree pollen season.  Noah’s peanut component testing showed a low level to component #2, but a high level to component #8.  A follow-up allergy test also showed that Noah is allergic to birch tree pollen, too.  Taking all this information into account, an allergist was doubtful that Noah was truly allergic to peanuts and scheduled an oral food challenge in his clinic.  Noah ate every dose of peanut and did not react.  His was “undiagnosed” with peanut allergy, and attends school without an EpiPen or his parents having to worrying about him reacting to peanut.

Situations when peanut component testing would be helpful1:

–        the patient has a history of mild peanut reactions in the past, or has never had a reaction to peanut

–        the patient now has an allergy to birch tree pollen

–        a classic or “total” blood allergy test to peanut is 0.35-15 kUA/L (middle range)

–        school-aged children

Situations when peanut component testing would not be helpful1:

–        the patient recently reacted to peanuts

–        the patient reacted to peanut a long time ago, and the peanut blood test is now 15 kUA/L or greater

–        the peanut blood allergy test is >25 or <0.35 kUA/L (very high or very low range)

–        children not yet in school

 

Allergy trivia:  peanut proteins are named based on the scientific or Latin name for peanut, Arachis hypogaea, and given a number.  Component #2 is called Ara h 2, component #8 is called Ara h 8, and so on.

 

1.  Sicherer SH, Wood RA. Advances in Diagnosing Peanut Allergy. Journal of Allergy and Clinical Immunology: In Practice 2013;1:1-13



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