Allergy Blood Tests

Over the last couple of weeks, we have discussed the importance of having a complete medical exam for a proper diagnosis of food allergies.  One method of diagnosis may be through a skin scratch test (You can read the specifics of an allergy skin test, including the strengths and weaknesses of that method, here.).  The next logical step in a comprehensive allergy picture is testing via a blood test.

What is an allergy blood test?

Allergy blood tests detect and measure the amount of allergen antibodies present in your blood.  Naturally, when your body deems something as an invader (virus, bacteria, allergen, etc.), it makes antibodies to attack the invader.  The antibodies release chemicals into the body to signal that an invader has entered your system.  In the case of allergies, the symptoms that you experience are triggered by these antibody chemicals, called Immunoglobin E (IgE).  Specific allergens are mixed with your blood sample and viewed for the release of these antibody chemicals.

RAST test is the most common allergy blood test known, however there are other tests, such as ELISA.  One source I read said that since the introduction of the Elisa test, Rast is rarely used anymore.  While allergy skin tests are the preferred method for doctors because of quick results and lower costs, there are benefits to allergy blood tests as well.

Benefits of Allergy Blood Tests

  • Blood can be tested for allergens even if allergy medication is in use.
  • A needle draw may be more comfortable than a longer series of skin pricks.
  • Patients with severe eczema make skin testing difficult.
  • As a means to support or refute skin test results.
  • Safer method of testing for patients highly anaphylactic to specific allergens.
  • Blood tests give more specific numbers on allergy sensitivity than skin tests.  Can be used to watch for trends, particularly of outgrowing certain allergies.

Disadvantages of Allergy Blood Tests

  • Cost more than skin tests and some health insurance will not cover blood tests.
  • Results can take up to 2 weeks.
  • Blood test results can sometimes be overly-sensitive and result in false positives.  Oral challenges are useful in this situation.
  • There is always the risk that a test is not sensitive enough, which results in false negatives.  Again, oral challenges may be necessary to rule out an allergy.

My Son’s Experience with Allergy Blood Tests

As an infant, I requested my son have a blood test after I realized the allergist only tested him for a few food allergies and not all the most common allergies (we no longer use that doctor).  She reluctantly agreed.  In addition to his peanut, dairy, and egg allergies, his blood tests came back positive for wheat and almond.  I believe both of those results were false positive as he quickly “grew out” of them at later skin testing, but I am not certain of this assumption.  In the last year, we have resumed blood tests, in addition to skin tests, at the request of his allergist.  She wants to see more specific numbers in order to start watching his trends.  We saw a reduction in all his IgE numbers this fall from last spring, but they are still positive.  His dairy allergy, in particular, is quite high.  He will continue to get an annual blood test (and a bi-annual skin test) as long as the doctor deems it necessary.

There are many new allergy panel tests coming onto the market (panels test for 200+ allergies).  I do not have a lot of experience with them as we have gone the traditional route in allergy testing.  I hope to be able to address these new tests next week.

What is your experience with allergy blood tests? Have you used it solely in allergy diagnosis, as a secondary back-up test to skin testing, or not at all? Please share your experience here as we all learn from each other.

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8 Responses to Allergy Blood Tests

  1. We have done some IgG and some IgE testing. I used it more as a basis to support what i already suspected, and to try new foods to remove as possible triggers (the test helped limit the playing field a bit, which was nice). What we haven’t done is IgE for food, only environmental, that’s to come. Our tests pretty clearly pointed to leaky gut as there were SO many things registering. I also knew test results were a gray area, and that I needed to use elimination diets to truly test anything…the only real fool-proof method for intolerance allergies. i am glad I did it, but if you do it, make sure it is through a reputable lab, and hopefully have the assistance of a medical professional of some kind to help you interpret the results. this was the hardest part for me…insurance doesn’t cover naturopathy, so i have not been able to find a Md who is well-versed in food allergies and intolerances…so very frustrating to feel like I have to play dr and figure it all out on my own….STILL trying to do that!

    • Cook says:

      I feel as though I act as the doctor quite often myself, and for more than just allergies. Thanks for sharing your experience!

  2. Kristen says:

    I remember, as a kid, having to go get hundreds of shots on my back to test for lots of different things. Tested positive for mostly seasonal allergies and a mild milk one…..got allergy shots for years and thankfully outgrew all of them!

  3. Denise says:

    Have you tried to modify the child’s diet based on their blood type. I wonder if the blood test showing the allergies are the same as the sensitivities to the blood type. The book is called “Live Right for Your Type”. Also check the Japanese journal studies based on allergies. These can be quite helpful.

  4. Denise says:

    My eldest daughter was eating baklava from a Greek pastry shop once, and my youngest daughter was seven at the time and wanted to taste the pastry. It was a matter of moments before she started salivating and chocking. Her face was turning another color and her tongue started to swell. She was going into anaphylactic shock. There happened to be an emergency vehicle in the parking lot where we were and they came to our aid. They started to triage her and rushed her to the children’s hospital. We happened to be down the street from the hospital. This was her first episode with a severe allergy attack. They treated her and she responded very well. She was given the blood test, but she was found to have very little sensitivity to peanuts, just sensitive to tree nuts. She has eaten peanut butter prior to test without any trouble. The doctor at the time did not not think the test show a high allergy to the nuts in the pastry, but yet and still it happened. Last year we were at a art festival and they were giving out samples from a organic company. The product said allergy free. As soon as she tasted the product a negative reaction started. I had her epipen in the car, so I started her to spit out everything and wash with water. They employees called the EMS that was standing by for standard procedures at festivals. She was taken to the hospital, given the same procedure as the last time. The doctor commended me for having her spit and rinse. Because her blood tests came back for low sensitivities. My background is telling me there are other components use in the factories or processing of these foods that are hidden to the public. I do know that a lot of the allergies we are seeing now is caused by additives or unknown items put into the foods. Now I am on a mission to find out the causes. I do a lot of raw nuts at home and will season my own and baked them for about 10-15 minutes. These do not bother her. She also reads labels before eating foods. We do a lot to keep our immune system up to fight disease or illnesses. She is older, so she becomes proactive for herself. Even though I have used the blood-type book for myself successfully, I will now apply it to my daughters diet. I have taught her to make her own foods treats at home. She likes to cook and learn about whats in the foods. Even though, I have a nutrition background there is always more to learn.

    • Cook says:

      Thanks for your story, Denise. Like I said, no one method is foolproof. My son has had false negative test results and failed “trial” food challenges. His doctor said that I should always listen to how he feels after eating something, even if the tests say otherwise. He knows what his body is trying to tell him. And you’re right, it’s scary the stuff that does not have to be listed on labels because it is an ingredient within an ingredient. That’s why plain, good ol’ real food is the safest route. Very interesting about the raw nuts that do not bother her. That makes it so hard to get to the bottom of it. I’m glad to hear your daughter is interested and able to be proactive for her safety. That is so very important and somewhat of a scary jump us moms of younger children will be facing soon enough.

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