RAST Testing for Allergies....What's the Point?

This is my rant about the RAST test....

What's the Point?!
 When my children were diagnosed with allergies (both environmental and food allergies), these diagnoses were made with the skin test.  I had heard other parents talking about their child's RAST numbers from blood testing and asked my doctor why she was not recommending these tests for my children.  Her explanation was that the skin test in itself was a reliable, accurate test for allergies and the positive skin test was enough of an indication to diagnose the allergy.  She explained that the RAST test would not really provide any more valuable information.  Apparently, the numbers are meaningless in that they cannot predict the severity of future reactions.  

Over the last year, we have been through a lot with my daughter's food allergies.  A life-threatening anaphylactic reaction to almonds really shook us as a family and we were humbled by the threat that these types of allergies pose.  We met with our peadiatric allergist for retesting (apparently the negative skin test to tree nuts was inaccurate)...the retest confirmed her allergy.  We tried several BIE treatments through our naturopath to "clear" her allergies.  I will write another post about that experience soon!....  Even skin contact causes our daughter to react and she has had hives on several occasions from touching something that was contaminated.  So...at our last peadiatric allergist appointment we decided it was time to do the RAST test.  
We were unclear as to the severity of her allergies with the skin tests...the doctor explained that for some children with very sensitive skin and eczema, they can have false positive skin tests because their skin simply over-reacts.  Even the negative control scratch would have some reaction.  Hopeful that perhaps one of her food allergies could be negative after the BIE and another year passing, I said "Let's do it".   My doctor prescribed EMLA cream to numb the area prior to the blood testing.  Unfortunately, the pharmacist convinced me not to use the cream because she said the bandaid type sticker that you put on with the application of the cream is actually more painful when removed than the needle would be itself.  This was bad advice according to my friends who have used the cream for their children and found that they didn't even flinch when given their needle.  My poor daughter found the blood test excruciating.  7 viles of blood were taken, a bill of $315 (can you believe that this is not covered by OHIP for a life-threatening condition?), and a three week wait for the results.....

Finally, the doctor called with the results....and guess what?!  They were USELESS!  The test provided me with a bunch of numbers that basically mean nothing and although some foods that we believed she was allergic to came up negative, new ones that we didn't think were a problem were positive.  How disappointing.  My doctor explained that her numbers were considered moderate and that meant that there is a chance she can outgrow the allergies perhaps in her teens....

Frustrated with the seemingly wasted effort and pain of getting this test performed, I googled for information regarding the results of these tests and their significance.  I found a site called Lab Tests Online: A Public Resource on Clinical Lab testing from the laboratory professionals who do the testing.  Here are some snippets of the article on RAST testing: (for the full article CLICK HERE)

Allergy Blood Testing

Also known as: RAST test; Radioallergosorbent test; Allergy screen
Formal name: Allergen-specific IgE antibody test

How is it used?

The allergen-specific IgE antibody test is a blood test used to screen for an allergy to a specific substance or substances if a person presents with acute or chronic allergy-like symptoms. This is especially true if symptoms are recurrent and appear to be tied to triggers, such as exposures to particular foods or environments, and if other family members are known to have allergies. A variety of different types of allergy tests may be performed by exposing a person to different substances under careful medical supervision (see Common Questions). The usefulness of these tests, however, can be affected by skin conditions, such as significant dermatitis or eczema, and by medications, such as histamines and some anti-depressants. With some tests there is also the potential for severe reactions, including a severe reaction that may be life-threatening. In these cases, the allergen-specific IgE antibody test may be ordered as an alternative, as it is performed on a blood sample and does not have an effect on the person being tested.
 A test may also be ordered occasionally to help evaluate the effectiveness of immunotherapy or to determine whether a child has outgrown an allergy.
The allergen-specific IgE antibody test may also be done to monitor immunotherapy (desensitization) or to see if a child has outgrown an allergy. It can only be used in a general way, however, as the level of IgE present does not correlate to the severity of an allergic reaction, and someone who has outgrown an allergy may have a positive IgE for many years afterward.  So what's the point?

What does the test result mean?

Negative results indicate that a person probably does not have a "true allergy," an IgE-mediated response to that specific allergen, but the results of allergen-specific IgE antibody tests must always be interpreted and used with caution and the advice of the doctor. Even if an IgE test is negative, there is still a small chance that a person does have an allergy. Elevated results usually indicate an allergy, but even if the specific IgE test is positive, a person may or may not ever have an actual physical allergic reaction when exposed to that substance. The amount of specific IgE present does not necessarily predict the potential severity of a reaction. A person's clinical history and additional medically supervised allergy tests may be necessary to confirm an allergy diagnosis.

If you can explain to me the point of this testing, please leave a comment to share!  I would love more information! 


  1. Thank you for posting this. I had a reaction to nuts a short time ago after having no history of being allergic. I had the RAST tests done but they came back negative. I was beginning to doubt myself but definitely experienced swelling of the tongue, etc after eating them. Although I am yet to have my skin test but as you'd know they are quite costly, I was worried that I may be overreating by getting it done.

  2. Wow, that's rather upsetting. I friend has food allergies so she did allergy testing in Boise, ID on all of her children. Good luck!

  3. I think some information you might like to know is that the skin prick test (SPT) has unlimited reimbursement for your doc. Doc's don't like blood testing because they don't make as much money. Your PCP would never do SPT. Remember that with SPT they are actually using the allergen. Your child could actually have APS while at the office. Allergists will rarely if ever use SPT for nuts or latex. If you talk to docs from Europe they think we are barbarians for making our children suffer. I find it interesting that drawing blood was more traumatic than having 50 needles inserted in her back and then having the red itchy reactions.

    1. My 1 yo didn't even cry when they took his blood for testing whereas I had a very itchy and swollen arm for a week (I'm allergic to pn, tn, and every thing environmental that can possibly be tested) from a spt

    2. I had the opposite experience. The skin prick test was a breeze, but it took three nurses (and me) to hold down my 18-month-old to get a blood sample. And then the blood test results told us very little about his actual allergies.

  4. You are spot on with your conclusion. Many of the reactions to foods and additives fall into the category of "Food Sensitivities", which are not a violent food intolerance or true food allergy. Food sensitivities can be additive; eat 5 five foods to which you are sensitive, and you will feel the negative impact. Eat one food to which you mildly react, and it may go unnoticed. I have used the IgG4 test to identify problem foods and have been shocked at the results. Avoiding these foods which I have been eating for many years has helped greatly. Next tests to be done are the Mediator Release Tests, which studies have shown a high correlation with offending foods/ingredients, with few false positives. You might research these tests to determine if they are more appropriate to your needs.

  5. Here's my counter-rant (sorry!)
    I will agree, definitely, that IgE blood testing is NOT definitive. There can be false positives and false negatives. However, skin testing is invasive and I believe it can actually create sensitivities where there were none. You mentioned your child's negative result to almonds, but then later they had a reaction and the second test showed the allergy. To me, that sounds exactly like the SPT sensitizing her to almond, then she had an actual reaction and the result showed up, later, on the second test. Though it is rare, anaphylaxis can, indeed, be caused by a SPT, right on the spot. (Sure, it's like a 1-2% chance, but it shows how the system is directly confronted with the allergen.) An SPT can be a painful, itchy, uncomfortable procedure (I have had it done, myself, just to see how it all worked/felt.) I also feel that the SPT I had sensitized me to several things I never had an issue with before the SPT. Also, people shouldn't be doing SPTs for 50 different foods nor should they do blood testing for a long list of random foods, either.

    I made that mistake, myself, with blood testing. I tested all these things that I was just curious about, that showed mildly positive results, yet were false positives. I think, all things being equal, it's a more gentle process to do a single blood draw (sure, needles are no picnic, but neither is a whole stack of them on your arm/back) and test only for foods to which there has been an observed or suspected reaction. For peanut, for example, you can do component testing (Ara h 2, Ara h 8, etc.), which is a bit better, but sure, not 100%. I figure if neither test is going to give me an iron-clad answer, I might as well go with the blood testing route and not expose my daughter to a bunch of allergens. So many of the current studies are coming out about sensitization beginning with the skin, so I am curious why this hasn't been taken into consideration by allergists. I think they keep doing SPTs because they are quick and easy (for them). That's not the proper basis for choosing a test method.

    Also, you can track IgE, over time, and gauge trends. You can't do that with SPT results, because they are so subjective. One doctor might call a wheal a "3+" whereas another would call it a "4++". (Yes, I know they are supposed to measure, but I have seen allergists just eyeball them and call them out.)

    One of these days, a better test will come along (hopefully Basophil Activation Testing), but for now, IgE is the closest we have to some sort of answer, so that's my point in testing every year.

  6. Read Dr. Scott Sicherer's book "Food Allergies: A Complete Guide for Eating When Your Life Depends on It (A Johns Hopkins Press Health Book)" or his book "Understanding and Managing Your Child's Food Allergies (A Johns Hopkins Press Health Book)". He is a top researcher and pediatric allergist out of Jaffe Food Allergy Institute at Mt. Sinai in NYC. He has entire chapters on testing, how its limited, and what to expect. I manage multiple food allergies between two children (peanuts, tree nuts, sesame, egg, fin fish, shell fish, dairy and soy) and our allergist did RAST and IgE testing, in addition to talking to me about my girls' health histories and assessing genetic factors based on other members of the family who suffer from allergies. She's gotten our diagnoses correct but it was a multi-step effort. No one test told us everything. We're now 8 years into our food allergy journey and my children's allergies have changed significantly from what they were when they were younger (they are currently 7 and 9). I've learned that there are no definitives when it comes to food allergy testing and diagnoses, just guidelines. Environmental allergies can greatly impact food allergy testing results as well (i.e. birch allergies can make a person test positive for tree nut allergies even if they may not be allergic to certain tree nuts).

    1. Thank you for writing your comment. I've been looking for resources like these.

  7. I think the combination of the skin test and the RAST test are more telling than any one test alone. My oldest daughter is allergic to peanuts and her RAST is high and her skin test is positive. My youngest had a positive skin test but a negative RAST test....therefore we will challenge her. Had I just listened to the skin test I may have been misled.

  8. Your daughter takes cues from you about what to be afraid of. Fear is probably the worst part when it comes to kids and needles. Try to calm your own emotions before any medical procedure for your daughter's sake, whether or not you are comfortable with YOUR DECISION.

    It is rough being an allergy mom, putting your kids through tests, denying them foods, finding and making special foods, pumping them full of medications after you spend valuable money on organic produce etc. etc. etc. You know what I mean. But it is also very stressful for the kids. I am hearing now about kids who develop anxiety because of their allergy and asthma experiences.

    Please remember you and your doctor are doing your best.. There are a lot of us out here who understand sometimes you need to rant. Once you've done that, try to stay positive. Good luck!

  9. Good Post. If you want to do Allergy blood testing online then you can contact MediAngels.com. They provide Online Blood Test service with affordable cost and also provide online medical second opinion from experts.

  10. Rast testing will show things that she may react to, even having lower to minimal levels can overwhelm her system. As for the cream for her eczema, please don't put her on topical steroids or steroid type creams. Coming from personal experience, and I'm on the severe side of having eczema, full body head to toe. One wrong meal, stress will set me off for months. Regardless, having her eventually stop the creams like that will have worse withdrawl symptoms. TSW or topical steroid withdrawl is even more painful then avoiding certain types of allergens. My RAST test came back with small amounts of reactions for everything and certain ones severe. My body however, doesn't get a break from reacting, whether or not I'm showing reaction symptoms.


You're awesome! Thanks for sharing your comment!