Monday, March 19, 2012

Competitive Parenting And Blue-Ribbon RAST Scores

Several years back, my family had the opportunity to participate in a Children's Memorial food allergy benchmarking study. (There's more about that in my post on FAHF-2 here if you're interested.) One of the really great things about the study was that we often got to meet other food-allergic families in the waiting room, awaiting their turn for poking, prodding, scratching and blowing into tubes.

Most were great, but I do remember one mother leaning over and asking "what is your son allergic to?" I rattled off the list of allergies. She then said "My daughter is allergic to cashews. Deathly allergic. She has a RAST score that's over 100!" I must have looked puzzled because she followed up with "It's off the charts!"

I was feeling pretty weirded out at that point because she was so ebullient about it all, but I waded in anyway. "You do know that RAST measurement has nothing to do with the severity of an allergy, right?" I said. "Its real purpose is for initial diagnosis, and then to determine the pattern of a child's immune response."

She bristled a little at this point. She was clearly not going to give up on the idea of her daughter being a outstanding test taker. "That's not true," she asserted. "The higher the number, the more allergic the child!"

((sigh)) What is it about our competitiveness with our children that makes us extend it even to their medical test scores? I was not a bitch that day - I let it go - but it's bugged me ever since because it's a very common misconception in our community. In the interest of getting it out of my system, let me explain what I know about RAST testing.

When a person becomes sensitized to an allergen, the body produces a "soldier" molecule called an antibody that grabs on to the allergen as soon as it comes into the body. A RAST test simply measures the number of these antibody soldiers floating around in the blood. (Wikipedia has a good summary if you're new to all of this.)

Once a certain number of antibodies are running around, there's a much higher likelihood that the "soldiers" are really there to cause problems. Doctors use what's called a Positive Predictive Value (PPV) to determine how big the "army" needs to be to predict a true allergy. Each type of allergenic food has a different PPV:

95% PPV (kU/L)
Note that these values are different than class references. Classes are ranges specific to the type of analyzer on which these tests are run, making it difficult to compare results from different analyzers/labs.

It's much clearer to refer to your child's RAST test numbers using the quantitative values ("a RAST of 30kU/L to fish", rather than "Class 3 to fish").

Nonallergic people don't have standing immune armies to foods. However, just about everyone will show small levels of sensitivity to a few environmental or food allergens on a RAST test, even though the positive result is under the PPV and has no clinical significance.

In a child with a RAST above the PPV for that particular food, there is a 95% likelihood the child will be allergic. However, that still doesn't determine how his or her body will actually react! Just as with world politics, there are different kinds of immune "armies" in the body. Will the reaction be like the India/Pakistan border skirmishes? North Korean saber rattling? European world war?  While we don't know what factors do provoke all-out immune responses, we do know that the size of the antibody army does not determine the aggressiveness of response. Once your child's number is above the PPV for the food, the size of the number no longer matters.

There are also some armies that just never fight, regardless of how large they are. False positives on a RAST are most commonly caused by cross-reactivity with environmental allergies. A RAST test should only be used in conjunction with a positive history and/or skin prick testing/challenge testing. When doctors see the "large army" on the RAST and the "skirmish" on the skin from an SPT, they can feel pretty confident in saying the child is likely to have a true allergy.

Some children show many positives. However, some of the positives are simply armies are left over from previous fights, or armies that were formed and never used. It can take a lot of additional testing, history and challenges to determine which antibody armies are  really active for these kids. (As I said in a previous post, if your doctor runs a "full panel" on your child and hands you a long list of positives without further testing or explanation, they are not doing their job!)

Keep in mind that no testing is perfect and challenge tests are the gold standard for determining allergies. These generally aren't done when children are small, both because they cannot articulate their symptoms well and because their immune systems are still developing. However, once a child is of an age to be able to accurately report what he or she is feeling, challenge tests are a very important diagnostic tool. Rather than fearing these as parents, we should expect them.

So why does your doctor keep doing RAST testing even after your child is diagnosed? For many children, a drop in RAST level may (MAY!) signal the beginning of tolerance. Your doctor may periodically do RAST tests to see what patterns show up.

This is where I see a lot of heartbreak with parents. "My daughter's RAST numbers went way up this year" is a common lament on support boards. What you should know is that doctors expect RAST numbers to grow along with the child. Up until around kindergarten age, RAST numbers continue to climb simply because the child is adding more immune cell to their body.
A high RAST does not necessarily mean your child is in more danger from a serious reaction. A rise in RAST does not mean your child is somehow becoming more allergic! 
While we all hope to see a drop in our child's RAST numbers at some point, it also is not the entire story. Doctors now think that tolerance to allergenic foods may depend more on the development of "good" immune molecules like IgG4 than on a decrease in IgE antibodies. Also, tolerance to baked milk and egg proteins does not relate at all to RAST numbers. Children can have a very high RAST and still pass a baked challenge.

Over the years, I've come to look at RAST numbers strictly for their entertainment value. It's a viewpoint I highly recommend. They're certainly not worth crying over...and they're definitely not something to brag about.

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  1. Love this easy to understand explanation. We stopped doing the recommended annual RAST several years ago. It wasn't worth the trauma and didn't really give us helpful information. My child can eat several foods he is "supposedly" allergic to. RAST testing has a place in diagnosis, but it's certainly not definitive.

  2. I just found your blog. Thank you so much for this! Our allergist is really busy and doesn't spend a huge amount of time explaining things so I found this to be a wonderful resource. My 2 year old son's milk had been 0.74, then 0.45 (which I was super excited about!) and then just went up to 1.26. I was, of course, crushed but now feel a ton better after reading this! The allergist actually said that we can try a baked challenge at home because his number was under 2 and this morning I gave him some Pepperidge Farm Cinnamon Swirl and there was no noticeable reaction! Can't wait to go through your archives. Love your writing and sense of humor. I feel like we would be fast friends in real life. :)

  3. I'm so glad it was helpful, Ali! Just keep in mind that a child can still be allergic even if that number is not above the PPV. However, a 1.26 is still really, really low and your son has a really good chance of outgrowing quickly.

    Pepperidge Farm CS bread seems to be the first thing we all try for baked milk! I don't remember which post it was on, but I did figure out the milk content per slice and it's next to nothing. We're up to 1/2 cup milk in a pan of brownies now, which is still only about a teaspoon per brownie.

    Glad it made you feel better. :)

  4. I was horrified to see my daughter's peanut score go from being in the 20s to being 100+ from one year to the next. The allergist was careful to assure me that it the allergy wasn't necessarily worse, nor was I somehow responsible, but he said that the rise was an indication that the peanut allergy was highly unlikely to ever be outgrown. Does that sound right to you?

    I've just found you and so I'll be catching up on all your posts. Thanks for your level-headed approach!

  5. Laura, I'm not a doctor! I can only tell you what I've heard through the grapevine over time from doctors and mothers. You should definitely follow up with your own physician for a clear answer.

    That said, unfortunately, it does seem like high numbers correspond to persistent allergies much of the time. There's always a glimmer of hope for outgrowing - you'll find the crazy stories about there about kids with really high numbers who still eat peanut - but your doctor is telling you what happens the vast majority of the time.

    I know how hard it is to think about this as being forever. If you haven't read it, I suggest you read "The 5 Stages" post I did. It talks about this mourning period. It can really be a hard time - I knew a lot of moms who ended up in out-and-out depression. It's so hard to think of this as forever for your child.

    AT THE SAME TIME...take a breath. My son is in a clinical trial at the moment for a new medication called FAHF-2. I really have a huge amount of hope for this one. Children who are being diagnosed right now will likely have a cure by the time they're leaving home, if not sooner.

    Just take it a day at a time if you can and try not to borrow trouble from the future. :) I'm glad you found my blog!

  6. P.S. A lot of moms are talking about this test right now:

    It's something you might ask about for a future visit. For a small segment of people, they find out their child has a really high RAST response to a protein that's not terribly allergenic.

    Unfortunately, most people seem to find out what they already suspect - their child is allergic to the bad ones. :(

  7. No worries, I'm far past the panic over it (the 100+ jump was probably 5 years ago), but I was just wondering if that jibed with your understanding because your post made me rethink what I thought I knew about RAST (you have a pretty good understanding of RAST stuff!)

    We've never had a confirmed reaction, but one of her anaphylactic reactions might have been peanut (she was a toddler and they were found all over the floor, but has multiple allergies and the situation was a big uncertainty). She is afraid to ever challenge peanut, and I've always said I didn't think the doc would ever want to challenge with a score that high, but reading your post made me realize that's not necessarily the case. I hate the not 100% for sure allergy that still makes you quake. Sometimes I fear MORE that I'm going to find out she was never really allergic to it. I'll look into that test. Very interesting stuff.

  8. Food Allergy Bitch, where have you been the last 5 years of my life??? I just got home from the allergist and yes, hid in my garage CRYING. So 5 years ago I gave my girl french toast-she got a rash. I had no frickin clue wtf was going on. Called doc-said don't give her anymore egg til she's 1. she touched meringue and had a minor reaction. Took her to the allergist where they FREAKED me the f out and said, "are you aware of how dangerous food allergies can be?? carry an epi-pen at all times and btw she's allergic to peanuts and treenuts. See you in a year and go to our support group meetings. Bye now" Yeah-ever since then, I kept her from all eggs, nuts, peanuts, yadda yadda. One year her numbers for egg were 8 and I did a cartwheel, this year they are 38 and her nuts above 100. I don't GET IT! the docs don't make sense to me and I swear I'd love their job bc you apparently don't have to have any answers. I am so happy to see your blog and know I am not alone.

  9. I'm so sorry...that sounds rough. It's always really hard when the numbers go the wrong way.

    If you haven't, you might want to look into baked egg introduction. It doesn't seem to have much of anything to do with RAST score -- 80% of kids with a milk or egg allergy can tolerate baked, and it's been shown to accelerate tolerance (for kids who are going to become tolerant).

    This is for milk, but the process/results are similar for egg:

  10. I asked my allergist about that and he guffawed at me! Your post gives me hope that those numbers don't mean anything. I'm ready to give her a muffin already! She never had a problem before. What if I'm making her allergy worse by keeping her away from it? Im checking your link rt now! Thank you!!

  11. Momofnatiandalex...I know it's frustrating, but you're really better off finding a new allergist you can work with if that's possible.

    You do have to remember that 1 in 5 kids fails the baked challenge, and the ones who fail can have a severe reaction.

    I'm embarrassed to admit that we did the impromptu "challenge" at home when my son was little. He had a REALLY severe reaction, one we weren't really prepared to deal with. We were sure he had outgrown milk and he wasn't even close. I know how tempting it is...but we take the challenges very seriously now.

    I have a lot of hope you guys will have success with a challenge, but it does need to be done with the help of an allergist. Call around your area and ask whether the practice does in-office food challenges for baked milk and egg and what criteria they use. This is *really* new thinking/research, so not all allergists are on-board yet, or even aware of the research.

    The other thing you can try is a hospital-supervised desensitization trial. Here's another link about the egg trials:

  12. Food Allergy Bitch, Thank you so much for this encouraging blog. Really loved reading this article. You encourage people who are dealing with this problem. God bless you. My 15 month old daughter had blood test and tested positive for many things. But her numbers are below five for most of the things. When I asked her allergist she didn't even tell me the levels. After seeing the report her allergist told me to avoid egg in the first place. But her report shows her levels are just 2.11. I am really confused with her allergist.
    Bookmarked this blog and will be reading articles from your archive. Thanks again,

  13. Vani, this stuff is confusing to all of us and good doctors who explain are difficult to find. Keep in mind, though, that kids with low numbers can still have an allergy! It's just testing alone in the absence of a history that should be suspect.

    Glad you found me!

  14. I know my 14mo old is allergic to peanuts. Saw the reaction to peanut butter, as well as the 15mm wheal on skin test. The peanut RAST is 13. Borderline to low-high. Does a relatively low, but still "high enough" peanut RAST mean less likely to outgrow, cuz it can't get much lower? Or more likely to outgrow, cuz 13 is closer to 10 than 73 is? Thanks.

  15. Unknown, your user name is very appropriate in this case... It's just not known which kids outgrow and why. Here's an article you might want to read about it:

  16. Wow! This article is amazing, thank you SO much for writing it. We have been at this for 2 years with multiple food allergies & so little direction! and from some of the "best drs" in the city. NO one ever mentioned an increase in good Igg4 could help reduce the food allergies. My son was born with an IGG deficiency, as he slowly grows out of it and his IGG's are increasing, his allergies are lessoning. But never once has anyone made this correlation. It makes perfect sense though. Is there an article that you may have read this in or did you hear it from your Doc...feeling really inspired and hopeful. Thank you, I cant wait to dig into your archives!!

  17. This is the best overview I've ever read on allergy blood tests. I got my results back in a letter but don't have a follow-up appointment until the fall!

    I also got a kick out of your take on competitive parenting. My tree nut allergy, which has been crazy sensitive throughout my life, came back with mostly "moderate" scores. I don't doubt there are smug parents out there who are certain their kid is more special than me because they're 100+.

    Thanks again for the explanation and the chuckles!

  18. Thank you so much for this excellent explanation. My 2 year daughter old had a RAST score of 9 a few weeks ago and all I got from my dr. was a one sentence e-mail telling me the number to avoid all peanut products. I don't even know if this is low or high. I have a really dumb question and hope maybe you know the scoop on this...until now, my daughter has been eating m&m's and other foods that "may contain peanuts" with no reaction. If I continue to let her have these in moderation while I'm present, am I helping her to build immunities? Or, am I causing her body to develop a larger army? I'm still in the desperate "please not my baby" denial stage. I see all of these recent studies on building tolerance so don't know if I'm helping or hurting? Thank God for people who have been through this and can help! Thanks!

  19. Hi Anonymous -

    I really suggest you go as soon as possible and see an a board-certified allergist. (If the doctor you saw WAS a BCA, see another.) It's really inappropriate for a doctor to give you so little support. Additionally, it is possible your child is sensitized to peanut (meaning tests positive), but is not truly allergic. This is a very technical study, but it shows that many children with RAST in your child's range do not have a true peanut allergy:

    That said...I am definitely not advising you to give your child peanut-containing foods. Peanut allergy has something called a threshold:

    It may be that your daughter is allergic, but that the residual peanut in M&Ms just doesn't tip her over into reacting. No one really knows if complete avoidance or small amounts is a better strategy, but the medical community seems to be swinging back again toward avoidance.

    All of this is complex, which is why you really need a doctor you can talk to! Ask your pediatrician for a recommendation, or join an on-line community and see if someone can recommend one in your area. Good luck!

  20. I have just returned from my gastroenterologist where I learned the results of two biopsies. I have been struggling with GERD, difficulty swallowing, choking, and a cough that has been with me for a year. I have food allergies and have done (I thought) a pretty good job managing them--no rashes, no headaches, no runny nose or sneezing, no laryngitis, no difficulty breathing, and congestion manageable. Well, it appears that my entire esophagus is inflamed from food allergies. The Dr. rattled off a very long name for this--which I cannot even begin to spell--and wants me to eliminate the top offenders from my diet for the next six weeks, as well as take the med he prescribed. My question is--an inflamed esophagus, really? Has anyone else ever dealt with this? Could it really be the cause of the difficulty swallowing and the choking? It kind of make sense, but an inflamed esophagus?


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