Why Peanut Component Testing Didn’t Work for Us


My six-year-old son is anaphylactic to peanuts. This we know with certainty because, after eating two bites of a PB&J when he was two years old, he experienced a swollen tongue and lips, congestion, runny/itchy/red eyes, vomiting, and head-to-toe hives.

Component testing cannot detect an allergy if the patient's IgE antibody levels are below the test's threshold
Do not get too excited about negative blood test results since those tests cannot detect an allergy if the patient’s IgE antibody levels are below the test’s threshold

My daughter was just six months old when my son had his anaphylactic reaction to peanuts, and the day after his reaction we became a peanut-free house and have been that way ever since. And with an older sibling who has a severe food allergy, the typical advice is for the younger sibling to avoid that allergen until age 5. Thus, my daughter was never given a taste of peanuts.

Two years ago as we prepared to take a trip to an all-inclusive family resort, I began wondering whether my daughter also had a peanut allergy and whether we should be carrying an EpiPen for her. The resort where we were going to vacation operated like a day camp for the kids. That is, the kids spend much of the day away from their parents in peer groups, and eat all three meals away from their parents. I felt the need to know whether my daughter also needed an EpiPen, especially since she’s shy and would be eating meals away from me and not prepared by me.

So we visited the allergist for a skin prick test and were a bit dismayed to learn that the results were positive for a peanut allergy. But, all in all, the news wasn’t devastating like it was with my son since we were already comfortable carrying epinephrine and living peanut-free.

Choosing a Peanut Component Test

Last summer when there was so much talk about peanut component testing in the allergy community, I figured this test would be perfect for my four-year-old daughter: she had never been exposed to peanuts but had a positive skin test and had been avoiding. What a great opportunity to find out for sure whether she was truly allergic. Or so I thought.

After calling around, I found an allergist in our area who would do component testing. When we went for the appointment I didn’t realize there were two different component tests since I’d heard about only the UKnow test. The allergist explained that the ImmunoCAP component test would test for a whole host of allergens, such as tree nuts, which my daughter also had never eaten, and that the UKnow test, though it was a more sensitive component test, would test for only peanut. The price for the two tests was similar, and because both are expensive, we had to choose between the more comprehensive food allergy test or the more sensitive peanut only test. We opted for the ImmunoCAP test.

The Results

ImmunoCAP results
The unreliable result of my daughter’s component testing: undetectable IgE antibodies to all peanut components (i.e., negative to peanut allergy)

When the results came in, the allergist interpreted them to mean that my daughter did not have a peanut allergy. The only thing, in fact, that she tested positive for was cats. The allergist’s proposed next steps were to redo the skin prick test and if the results were negative, which she believed they would be, we could do a peanut challenge at home (!). I was completely averse to doing a peanut challenge at home and didn’t want to deal with this allergist’s overly busy office for yet more appointments, so we found a new allergist.

Next Steps

Our new allergist came highly recommended. I took all of my daughter’s test results to the appointment, and was surprised to learn that he doesn’t even do component testing because, according to him, the results can be difficult to interpret. I had asked the first allergist about this: because my daughter has never been exposed to peanuts, could she have the IgE antibody for peanut allergy but at such low levels that they are undetectable by the test? The first allergist seemed to think this line of thinking was completely incorrect; however, our new allergist agreed that this was exactly why he doesn’t do component testing. He eagerly flipped through the component testing results since he’d never seen component test results before.

After taking her history and reviewing all the test results, our new allergist recommended an in-office peanut challenge so we would know once and for all whether our daughter was peanut allergic.

I’ll skip ahead and let you know that my daughter did not pass the oral food challenge, though her reaction was much delayed.


First, never do an in-home food challenge if your child or anyone in your family has a history of food allergies. If your family doesn’t have a history of food allergies but you’re uncomfortable doing a food challenge at home and your allergist refuses do one in the office, find a new allergist.

Second, if your child has never been exposed to peanut before, no test other than a food challenge will give you a definite answer as to whether your child is peanut allergic. My daughter passed the ImmunoCAP component test but failed the food challenge for peanut; the test was not sensitive enough to detect her IgE antibodies for peanut.

Of course I’m left wondering two things: 1) Would the UKnow peanut component test have accurately predicted the presence of peanut allergy had we opted for the more sensitive but less comprehensive testing? And 2) What do her IgE blood levels look like now? I’ll never know the answer to number 1 since she has now been exposed to peanut and her body has probably produced more IgE antibodies as a result. Because the ImmunoCAP test was inaccurate in predicting the presence of peanut allergy, I have zero confidence in the results of any of the other food or environmental allergens it tested – what a waste of money. (We already knew she had a cat allergy, which it accurately predicted, but she had been exposed to cats many times.)

As for #2, because I feel like I’ve put her through enough testing for one year, I won’t know her blood levels until we go back for retesting and, if we’re diligent and lucky, we’ll never know her blood levels immediately after exposure. Because her reaction was mild – which I’ll detail in tomorrow’s post – I’ll consider requesting the UKnow test the next time we go for blood work if sufficient evidence of the test’s reliability exists.

Tomorrow, I’ll post about her food challenge in case your child has never gone through one and you’re curious about how it works.


  1. Joan says:

    There is another possibility, which is that your daughter has a lentil allergy that is cross-reacting with peanut. Vicilin, the main protein in lentils, can cross-react and cause a slow-building peanut response:


    Your point is a good one, though. The test is experimental and all results have to be confirmed via food challenge.

  2. Nancy says:

    I see the results you provided only go down to 0.3 and I’m not familiar with the units provided. I do know the Immunocap Specific Ige tests are valid down to 0.1. Perhaps, if the instrument used had it’s parameters set to the lower linearity, you may have been able to see the small reaction you speak of. Also, if you had the luxury of seeing the raw data, you would have been able to see the Relative Units (RU’s) for each component which could have tipped you off to the slightest reaction despite the <0.3 result. The first allergist you went to was truly and surprisingly misinformed about the in vitro test. You were right in suspecting the lack of a positive response due to your daughter not having been exposed. I am only a med tech who performs allergy testing on the Immunocap and I am better informed than that overpaid allergist! Kudos to you for getting a second opinion.

  3. Jen says:

    I can tell you from experience that a food challenge is the only definitive answer. My son is allergic to peanut, milk, egg, and still GI sensitive to soy. His blood testing has showed a decrease in both egg and milk to the point that the last test he had both were undetectable. We challenged both of them this summer, with (negative) skin prick testing done before each challenge. He ‘failed’ both of them, with the milk challenge earning him his first epinephrine shot. (Face/neck/arm/torso hives from the egg which was treated with Zyrtec.)

    I honestly can’t believe that there’s an allergist in this country that would even think about suggesting an “at home” challenge. To be honest, I’d think about reporting them to the state medical board for negligence. :/

    1. Sorry about the negative testing but confirmed allergy for egg and milk. Yeah, food challenges are the only definitive way…but they’re so nerve wracking aren’t they??

  4. Chrissy says:

    I am currently waiting on the results of our UKnow test. I have twins who we immunoCAP test annually. Both test over 100 for peanuts (amongst a few other things) but only one twin has had reactions (multiple anaphylaxic reactions). The other child has never even gotten a hive. So we figured it was worth the cost to find out her likeliness to actual have a reaction. While doubtful, I’ve got my fingers crossed for some kind of good news.

    1. Oh, I hope you get good news! Identical twins? Epigenetics – or whatever it’s called – is so interesting, how kids with identical or near identical genes and environmental exposures can be so different. Best of luck!

  5. tom says:

    Immunocap is very accurate testing but in your case where the peanut component testing was negative it did not include testing for Ara h8, Ara h9 so not all the components were tested. There are case reports of peanut allergic individuals that have allergy only to Ara h8 so in this situation, having failed the peanut challenge suggests that this might be the answer!

  6. Kimberly says:

    Hi, I found your post here through reading about testing. I’m confused. You indicate that there are two different tests for indicating sensitization at the molecular level, uKnow Peanut and ImmunoCAP. I just received an information packet from my son’s allergist yesterday because we are interested in the uKnow Peanut testing. Both the website for uKnow Peanut and the printed brochure for uKnow Peanut both indicate the full name to be “uKnow Peanut ImmunoCAP Molecular Allergy Test”. I also called the company representative for uKnow who services our allergist and she confimed it was the same. ImmunoCAP in the registered trademark, and from what I was told, not a separate test. Can you please provide me any information that you have that indicates there are two different tests? Thank you!

    1. Hi, so sorry that I missed your question until today. Perhaps they are the same, but the allergist who ordered our test led me to believe that they were different. The branded uKnow test was not the test she ordered. The allergist told me that the “ImmunoCAP” test I reference in my entry was, “…still a component test but tests for more than just peanut.” Maybe the only difference is marketing/branding…but that’s weird since uKnow was marketed as new and many insurance companies wouldn’t cover uKnow costs but would cover the other test.

Comments are closed.