Although I’m not an allergist, I attend the annual Allergy Update medical conference for allergists every year in Toronto. This year, Dr. Robert Hamilton informed us that the presence of IgE measured by a RAST test is not predictive of the severity of allergenic response: In fact, it’s less than 50% predictive.
He advised that it is now possible to measure response to allergen components. Peanut has been broken into 13 allergenic components, with the component Ara h 2 giving the highest risk of a severe reaction. It’s the most important component for peanut allergy, and it can now be measured with a blood test.
Dr. Hamilton described oral food challenges as expensive and risky, and seemed to favor component resolved testing to help determine who is likely to have a severe reaction to peanut and who may pass a food challenge. He stated that positive IgE levels alone do not reflect whether or not a person would pass a food challenge, but that there are people with levels so high, it can be predicted with 95% accuracy that they would fail a food challenge and be at high risk of a severe reaction.
So even with very high RAST levels, there’s a 5% chance that a food challenge could be passed, allowing a person to then eat freely. I am having my son tested for the IgE antibody to Ara h 2 and the other allergenic components of peanut, in order to confirm or exclude his peanut allergy. If his level is below 0.1 kU/L, that would exclude the allergy. Apparently, even with a value of 2 kU/L, there is a 50% chance of passing a food challenge.
It was concluded that IgE antibody to Ara h 2 is a good predictor and adds to the quality of decision making. The ImmunoCAP, Immulite, or Hy-Tec by Hycor tests were recommended as they’re automatic analysers that use allergen specific IgE, separated from cross reactive molecules. I’m very pleased to see new diagnostic tools being added to my allergist’s toolbox.
The ImmunoCAP allergen components that can be tested for plant based foods (including peanuts, brazil nut, hazelnut, almond, cashew, macadamia, pecan, pine nut, pistachio, and walnut) are here: http://www.phadia.com/en-US/Allergens/ImmunoCAP-Allergens/Food-of-Plant-Origin/ You will see that peanut has been broken down into its allergenic components, as have Brazil nut, and hazelnut. Dr. Hamilton advised that they’re working on breaking down more tree nuts in similar fashion. Here is the ImmunoCAP requisition form: http://www.pirllab.com/pdfs/PiRL-Requisition-Form.pdf
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I don’t live in Canada, but this was really helpful info!
I have nearly 20 allergies, so for me to take this test and be certain of what exactly I’m allergic to would be wonderful!
Thank you!
Dear Elizabeth,
Thanks for posting this. Very clear, concise write up on a very useful and one-of-a-kind technology. For a perspective on how these tests can be used to help patients, please look at this post: http://www.asthmaallergieschildren.com/2010/11/13/new-allergy-tests-may-help-improve-life-for-people-with-food-allergies/
Thanks, I find this interesting, but I will need more time to follow all your interesting updates… I did not test yet my kids on any blood work. Doctors said to wait until they will be older.
Cinta
Eli did component testing through http://www.pirllab.com for his peanut allergy. It came back Ara h1 and Ara h2. “Anaphylactic” His blood level IgE went from 83.7 to a 62–which Dr. Nash said do not read too much into that number as it can change daily considering what’s going on with the immune system. I was afraid Dr. Nash would say, “He’s too allergic” to start desensitization but like me I guess he even saw a greater need as we KNOW what WILL happen. It’s just a question of when. Now he is consuming 600mgs. of peanut flour a day and has yet to have a reaction. Hopefully it will stay that way forever!!! Eli’s egg came back non-anaphylactic so we gave him a food challenge (I was relaxed) and he passed. We did not test him for scallop on the component. I would have but it wasn’t available for some reason at the time? He passed that food challenge also. That one scared the daylights out of me only because shellfish… we’d have to desensitize one at a time. And it’s airborne. So glad we only have our one peanut allergy and it’s going away slowly but surely.
Is this test only available for peanut or other allergies too?
Amanda