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RAST how accurate is it?

13 replies [Last post]
By Ethans_mom on Sat, 02-06-10, 02:04

My four year old son was diagnosed with a peanut allergy at 1.5 years old, after an anaphylactic reaction. His RAST test was 7.5 for peanut and .45 for Soybean. We have managed these allergies with avoidance, however he has developed asthma and has several hive outbreaks seemingly unrelated to soy or peanut. I just had his RAST reordered and his Peanut was 74, soybean was 17.8, Wheat 1.03, Corn 1.42, sesame seed 4.45. His total IgE was 205. Our allergist who we have seen once has moved, so we are awaiting an appointment with a new group. To say that I am stunned and unsure of how to feed him is an under statement.

My question is, is the RAST accurate? How could we go from 2 allergies in 2 years to most major food groups? Between corn, soy and wheat what else is there?

I know I sound frustrated, I just don't know where to start.
Thanks for any advice.


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By ElizabethY on Tue, 02-09-10, 00:51

I don't have an answer for you, but I can sympathize. When my son was diagnosed at 18 mos., his RAST was something like 4.5 for PN, and there were two tree nuts that were less than 1. At three, the RAST was 100+ for peanuts, and several nuts that were 4 or 5. I was devestated, felt like I was experiencing the diagnosis all over again, because I felt like now there's no chance to outgrow it.

Honestly, I don't know how accurate the RAST is. Personally, I don't place much stock in the numbers (although I would rather see them lower). That's my experience, for that it's worth.

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By jenniferbfab on Tue, 02-09-10, 04:02


This is my personal opinion. I am not a medical professional and I have no medical training whatsoever.

The RAST--in my uneducated opinion--is not "accurate" but it does indicate there is a sensitivity. Our allergist told me the numbers on the RAST don't have much significance. When my son's numbers increased, the allergist told us the only thing we can learn from the increase is that there is still a sensitivity. The numbers also don't predict the severity of reactions. In fact, my son is extremely sensitive to skin contact and ingestion but his numbers fall in the moderate range.

And don't forget the news over the last year about families who unnecessarily eliminated all sorts of foods due to blood test results only to learn later that their child did not actually have all those allergies. (See the recent WSJ article: http://online.wsj.com/article/SB1000142405274870380890457502501319464513... )

Did your son have a skin test for these allergies? I think positive skin test along with positive blood test would be more reliable. Even then, without a telling reaction following ingestion (for example), a food challenge is the gold standard.

Hope this info helps a little and that the new allergist can shed more light on this for you.

Best wishes,
Jennifer B

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By ElizabethY on Tue, 02-09-10, 13:08

That article is fascinating, and confusing.

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By BestAllergySites on Tue, 02-09-10, 14:04

Elizabeth--yes the article in confusing and keep in mind that it's written by a journalist. That's not to say there is not truthful information in it--it just it what it is--reports on what the journalist found.

These reports can come from various places and not even all allergists within a community agree on all things.

Leisa--I'm not a medical professional but can tell you what I know, what I've experienced and what I've been told by several well educated/respected allergists within the community.

1. No test is 100% accurate without a history of symptoms or a food challenge.

2. In the absence of the above--a blood/rast and skin prick test is more reliable--BUT could still be wrong.

3. Eczema can cause false positives on skin prick tests OR false high results.

4. Rast numbers are typically made up by the lab and don't really mean anything in theory however most allergists agree that a score over 14 indicates a higher likelihood of an allergy.

5. Very few individuals are actually significantly allergic to numerous items. It's not to say they aren't out there. When I say numerous--think 8-10 items or more.

In your situation--I too would question the results giving the food groups. Was the test administered the same as the last test that was administered?

6. Allergies come and go and change over time. Hormonal shifts are a prime time to gain or lose allergies. Younger children can sometimes have higher numbers that peak around age 4-6 and then start to go down.

7. This is important--allergic reactions can cause test results to be off. So if your child had such a reaction before testing--these numbers could be wrong. When an individual has a reaction--their body is more sensitive to another reaction for a period of days to a week after. Allergies are an immune system response--so think of an allergic reaction as weakening the immune system.

If your child is or has been consuming the foods that came up positive without reaction--I would discuss with an allergist. I hesitate to tell you to continue feeding the food. However, there are some who have become allergic to foods overtime after avoiding them for a period of time--so you need to be careful there.

I would keep a strict food diary of what he eats now and when he has a reaction to try to pinpoint what it is.

I would also get into to see another allergist asap. I hate to see you avoid these foods unnecessarily and potentially cause an additional food allergy by avoiding.

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By Ethans_mom on Tue, 02-09-10, 14:31

Thank you Ruth, Jennifer and Elizabeth,

I have had some time to process and read about the various allergies over the weekend. I know that we have life threatening allergies to peanuts. I have witnessed two episodes. He gets hives with soy products. However I am not sure of what may be triggering the asthma? His first lab test and last were the same test and used the same scale and same lab.

1. He has had 3 episodes of hives two weeks before we did the last RAST, so he may have a false reading due to his system being so inflamed.

2. He is not completely clear respiratory wise. Still some post nasal, but he has not needed any inhalers in the last few days. So maybe the wheat, sesame, or corn is aggravating his asthma. I just would like to know which one. The asthma is a recent diagnosis. Since September he has had needed treatment on and off with steroids and albuterol. He started pre-school half a day and has been catching all the respiratory bugs. I kept him home all of December and he cleared up a bit but still required breathing treatments frequently.

3. Should I keep him off all of them (corn, sesame, wheat) and reintroduce one, and if so how long should I keep him off before reintroducing one of the allergens? I really would like to clear off corn since it has been the hardest to manage.

4. The allergist appointment is weeks away.

Thanks again for the information.

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By BestAllergySites on Wed, 02-10-10, 15:57


I can't in good conscience tell you whether you should try an elimination diet with corn, sesame or wheat. I'm not an allergist and don't know your child's history.

I know the apt is weeks away. I would suggest calling to see you if could be called in the event of a cancellation OR asking if the allergist can call you back regarding these issues.

Very hard to say what could be causing the asthma. As you know, there are lots of asthma triggers. I would start by looking at any environment issues or changes.

For example--pets, dust mites, do you use an air filter, do you vacuum regularly etc.

Also, illnesses can make asthma worse and prolong it. It's possible that once you get through the illnesses and the season--his asthma will be better.

I say it's worth a call into your allergist. Sorry I can't of more help.


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By jenbug on Tue, 02-09-10, 17:40

I was wondering about the RAST test as well. My son ate a bite of a Reese's Peanut Butter cup on a Friday evening. He spit it out immediately and his left cheeked swelled, he started to wheeze a little bit so we gave him Benedryl. He was fine, I took him to see his Pediatrician on Monday and they did a Rast test. His numbers came back at a high 4. Could this be a false high because of his reaction 2-3 days prior. We do carry an epi-pen but I was hoping his result on the test would be lower next time. I asked about an allergist and they said he is to young to do testing on, he is 3 1/4. We stay away from all nuts and have not had a reaction since August 2009. Is is not allergic to anything else. I know it is a long shot but I still hope he may outgrow it.

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By jenniferbfab on Wed, 02-10-10, 03:46

My son was 3 and 1/2 years old, almost to the day, when he had a skin test which confirmed his peanut allergy. The fact that he was able to have a skin test contradicts what you were told, so I would encourage you to seek a second opinion.

I honestly don't know if the number could be a false high. That would be another good question for the allergist. I was sad to see my son's numbers have only gotten higher over time, but our allergist said the numbers don't mean very much. There is a threshold--which I am unable to remember right now--which they say means that a reaction of some kind will occur but the numbers do not indicate severity.

Allergic Girl had a good post about testing a while back: http://allergicgirl.blogspot.com/2009/01/food-allergy-testing.html

They say 20% grow out of peanut allergy, so there is a chance. If it does not work out that way, the treatments scientists and doctors are working on look very promising. I really believe something will be available before our children reach adulthood.

Best wishes,
Jennifer B

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By BestAllergySites on Wed, 02-10-10, 15:50


First off--regardless of the numbers and severity--based on what you wrote above--it sounds like your son has a true peanut allergy. He spit out the food AND had a reaction. In your case, it doesn't really matter what the numbers are b/c severity can change over time.

Most people are concerned about testing from a standpoint of whether they are allergic period-b/c they have no history of reaction but have positive test results.

It is possible that the numbers are higher based on a reaction prior to testing--but in reality it doesn't really matter at this point. Your child should avoid peanuts period.

My son was allergy tested at less than 2 years old. So your son could definitely be tested. However, testing is based on numerous factors including the child's maturity and ability to handle testing.

Hope that helps to explain things!

Edited to add: Jen is right in part. As I stated in my above post--the numbers don't mean anything in part AND they don't indicate severity.

However, (and this is coming from multiple allergists) if an individual has a rast of 14 or more (pretty sure it's 14) the likelihood of a reaction to the food is MUCH higher. Again, it doesn't tell you how severe. But the likelihood of a reaction is higher if the rast is over 14. Of course there are always exceptions to the rule.

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By jenniferbfab on Wed, 02-10-10, 16:00

Please keep in mind, the moderators here are moms of peanut allergic children but none of us are medical professionals.

We've all got at least a few years of managing peanut allergy (and other allergies, as well as asthma, eczema, and a few other things too!) under our belts, but the advice and information we provide here is just our personal opinion based on our experiences. Your allergist(s) are always your best and safest source of information for managing peanut and other allergies as well as asthma.

Jennifer B

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By BestAllergySites on Wed, 02-10-10, 16:08

Thanks for the reminder Jen!

I'd like to point out that is why I have that information/disclaimer in my signature and always have since I've been moderating here. ;)

As Jen said--please remember we are parents too! We try our best, but may not always be able to give you the answers you want or need.


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By Michaels Mom on Thu, 02-11-10, 00:57

jen bug, my older son was 2 1/2 when he had his 1st skin test and our allergist would have done one on our 9 month old if it hadn't been too soon after his reaction. Maybe a second opinion?

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By Michaels Mom on Thu, 02-11-10, 01:00

just b/c of the misleading info....I would want to know I was getting 100% accurate info from my child's physician- What Ruth said is the most important point, though!

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