Monday, June 11, 2007

The RAST Test

What is the RAST test?
Def from Medline Plus:
Medical Encyclopedia
RAST test
The RAST (Radioallergosorbent test) is a laboratory test performed on blood. It tests for the amount of specific IgE antibodies in the blood which are present if there is a "true" allergic reaction.
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Description of IgE Antibodies: The immune system produces at least five kinds of immunoglobulins (Ig) or antibodies (IgA, IgD, IgE, IgG and IgM), but the principal one that participates in allergic reactions is immunoglobulin E, or IgE.
Every individual has different IgE antibodies, and each allergic substance stimulates production of its own specific IgE.
An IgE antibody made to respond to ragweed pollen, for example, will react only against ragweed, and not oak tree or bluegrass or any other kind of pollen.
When the antibodies encounter the allergen they are programmed against, they immediately signal the basophils or mast cells to unleash histamine or other mediating chemicals into the surrounding tissue. It is these chemicals - mainly histamine - that cause the familiar allergic reactions.
Histamine released in the nose, eyes, and sinuses, for example, stimulates sneezing, a runny nose, and itchy eyes. Released in the lungs it causes narrowing and swelling of the lining of the airways and the secretion of thick mucus. Released in the skin, it causes rashes and hives. And in the digestive system, it causes stomach cramps and diarrhea.

Info from Riley Childrens Hospital
An allergy test does not diagnose allergic disease. The test determines the presence or absence of specific IgE antibodies. IgE is a necessary component of an allergic reaction.The physician must decide if the signs and symptoms of the illness are consistent with allergy.

Allergy tests are scored in a variety of ways. The blood tests are in classes 0 to 6 and skin tests are scored 0 to 4 plus. The score really has no relation as to how allergic the patient is. How allergic you are is more a function of what happens to you with exposure. Who would you say is more allergic, the patient who went into anaphylactic shock with milk ingestion and had a 2 plus skin test to milk or the patient who had contact hives or urticaria from milk who had a 4 plus skin test to milk? One almost died, the other gets an itchy rash. I look at the test results as an answer to the question- is there sensitization to this allergen? Yes or No?The value of the test again is as good as the history that supports it. It also may depend on what tool is used to perform the test and the quality of the allergen extract used. Also note that for foods, especially in the model of atopic dermatitis- a type of eczema, positive food tests are a 50-50 proposition. Half of the time the positive result may not mean anything clinically- the concept of a false positive. However, the negative food test has great "negative predictive value"- with a negative skin test there is very little chance that the food with cause a problem.

So why did I include all of the above information? To try and explain what the following means or doesn't mean for my son. He had the blood test done a few weeks ago and the results were that he is still allergic to same things as before and now we are adding tree nut to the list.
Most of his test numbers went up, but that is actually typical of children his age. And the school of thought is that numbers tend to go up before they come down.
This is the chart used for the blood test:
Specific IGE Class KU/L Level of Allergen Specific IGE Antibody

0 <.035 Absent/Undetectable
1 0.35-0.70 Low Level
2 0.71-3.50 Moderate Level
3 3.51-17.5 High Level
4 17.6-50 Very High Level
5 51-100 Very High Level
6 >100 Very High Level

For the Little Man, he is :
1.91 or a 2 for Casein (milk protein)
1.37 or a 2 for Milk
17.00 or a 3 for egg white
8.88 or a 3 for egg yolk
1.27 or 2 for Almond (new)
.44 or 1 for Brazil Nut(new)
1.80 or 2 for Hazelnut (new)
1.10 or 2 for peanut
63.20 or 5 for barley
9.68 or 3 for Oat (and this is new. Although we'll avoid, I think it's a false positive)
>100.00 or a 6 for wheat
97.50 or a 5 for rye

All these numbers mean are that my son is probably allergic to these allergens. We've seen reactions (and strong ones) to wheat, egg, and milk so we know for sure that those are correct. I hope and pray that I'll never have to see a reaction to any of the nuts. Just because a number is high doesn't mean my son will react violently if he eats it. He had a severe reaction to egg last year and his RAST score at that time was only a 2. It just means he is more likely to react to it. The high grain numbers also mean he is less likely to outgrow that allergy. Because I've seen a reaction that he's had to wheat and the RAST test number was a 3, you can bet the house that I will do everything in my power to be assured that he doesn't have another reaction now that he's a 6 though. Why press fate? The last one was horrific enough.
So that's the allergy test in a nut shell, no pun intended.
We will just keep doing what we've been doing. I've ordered 2 more cookbooks today and the peanut allergy book our Allergist recommended.
I'm also starting to plan the Little Man's allergy friendly 3rd birthday party. So for the next month, I'll bore you with the details of our fete. It will have a Thomas the Tank Engine theme and won't have any offending grains present that's for sure.


amy said...

Have I ever told you how much I learn from this blog?? and thanks again for the kind words on our baby name

Norma said...

This doesn't sound like much fun--raising kids is tough enough!

Aimee said...

Our boys and their tests - kind of makes my head swim sometimes.

thinking of you . . .

Stephanie said...

Found your blog with a search about false positive rast tests- hoping and praying ours are.... My son is 14months old and had a 1 month rash, we finally did the rast test last week and he came up class 2 for wheat and soy class 3 for egg, milk, and peanut. We go to an allergist for skin testing Thursday. Did you do skin testing? I have cut out egg and soy (he was on soy milk) from his diet and with a prescription cream his rash cleared. I'm having alot of anxiety right now about how aour life is going to change and what's in store for him as he gets older( and goes to bday parties). Thanks for posting your story.

ChupieandJ'smama said...

My little guy had an anaphylactic reaction to wheat and that's how we found out we had food allergies. We saw an allergist and he skin tested my son first. Several things came up as positive and then he followed up with the RAST to confirm everything. Did they explain to you how the skin test works?
Check out this page from Mayo Clinic for an explanation:

Make sure to bring some toys and books because your baby will have to sit there for 20 minutes while they wait for the skin testing to take place. It isn't painful but it may be a little itchy.

If you have any questions, feel free to e-mail me or you can check out the baby center food allergy board ( there are a lot of ladies with knowlege over there!
Good luck!!

Anonymous said...

I understand your fear for what is to come for your son. My daughter who is now 3.5 was recently diagnosed with several allergies. It all started when she was about a year and had pretty bad eczema, I went to several doctors who were trying to treat her eczema when one smart one said, lets do an allergy test. I think the test was a RAST test and she only came up positive for eggs. They told me that allergy testing in children under 2 isn't very accurate so keep her away from eggs and we'll revisit in a year. Well, I kept her away from eggs thinking that it was so hard, parties were a drab and planning meals was tuff too but Morgan was a trooper. We learned that going to birthday parties meant that with a little preplanning Morgan could feel just as special as that birthday child. Skipping ahead 1.5 years, her eczema was still so bad and Morgan was up most nights itching to the point that she would bleed. I was doing everything I was told but that poor kid still looked like she hadn't slept for weeks. We decided to get her tested again and she came up positive to trees, grass, mold, pollen, dogs, eggs, soy, nuts, all legumes including the only veg that she would eat, green beans, she is also allergic to tomatoes, oranges and peaches. I am starting to find more foods that she can eat after spending several hours in the grocery store. Also - the allergist said not to freak out about the soy, if it says contains soy then avoid it but we don't need to avoid the emulsifiers and soy oil. I don't want to tell you that you should or shouldn't avoid thoes things too but I think you can assess based on your son's reactions - Morgan's is a little itch and it ends up that she doesn't react to thoes small levels of soy. I could write for hours about this but have to go. Good luck to you!

Tini said...

I have spent 2 days trying to read on RAST scores as I mum who daughter who had one. Thank you for making this so clear.
My daughter has very high peanut allergy and tree-
nut allergies:I am so scared, anxious and reading this blog helps.
You are very brave.
Thank you

Jeffrey lin said...

Hi, I am so glad you seem to have a good grasp of managing your son's conditions. I also have severe allergies. My overall IgE is over 20,000 and most things i've tested for, my IgE is between 20 and 50, but with several in the stratosphere. I've suffered with this all my life, with reactions showing itself as eczema, infections, asthma, hot/coldsweats, internal swelling, etc. I just wanted to introduce myself and hope to stay in touch, especially if your family or your son just needs someone who's gone through and still going through the worst of the worst. It's not something easy for others to understand unless they've dealt with something similar.

I won't go on and on, but if you're interested, here's a blog post from when I was finally well enough to use my fingers to type. Also, I've been making video updates.

Keep in touch.

Jennifer said...

My daughter was tested for allergies. She was class 2 for corn, rice , peanut, hazelnut/ filbert, sesame seed, walnut, watermelon and tomato. Should I allow my child yo still eat some of these foods since she is a class 2. Please comment. This is the very first test and I am trying to find out more about this.

Jennifer said...

My daughter was tested for allergies. She was class 2 for corn, rice , peanut, hazelnut/ filbert, sesame seed, walnut, watermelon and tomato. Should I allow my child yo still eat some of these foods since she is a class 2. Please comment. This is the very first test and I am trying to find out more about this.

ChupieandJ'smama (Janeen) said...

Hi Jennifer,

I'm sorry your daughter was diagnosed with food allergies. Food allergy testing can be confusing. The numbers do not indicate the severity of the reaction. And each reaction can escalate with each exposure to the allergen. This question is really a good one for your allergist (it's recommended to see a board certified allergist who specializes in this). He may have you avoid the allergen completely, or he may want to set up an oral challenge to make sure that anything that you have not seen her react to are true positives.
For now I would avoid those allergens, but give your allergist a call to clarify how you should proceed.
Good luck and please email me if you have any other questions. My email is

Best Regards,