What is the RAST test?
Def from Medline Plus:
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.
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.