Monday, April 15

Food Allergy Blood Test: RAST Test Results

We finally got Little Guy's food allergy blood test results back and met with the allergist to review them. I'm shocked, annoyed, disappointed and yet hopeful.  Here's why...

I'm shocked and annoyed: Our insurance covers LabCorp for blood work. Our previous allergist who ordered the test did not know (or knew but did not tell us) that LabCorp does not have the "gold standard" food allergy RAST test (which I now know is called a  CAP-FEIA or CAP-RAST). Therefore, the blood test that I put off for 2 years and that was SUCH a big "to-do" isn't going to be as helpful as it should be. I wrote about the blood tests in this postThe test also didn't cover all the top 8 allergens (including various tree nuts).

I'm disappointed:  The RAST test showed he's allergic to everything we knew already (wheat, egg, dairy, peanut and sesame).  It also showed he's allergic to walnut - which he previously tested negative for in a skin test. But this does illustrate the inaccuracy of these tests!

I'm hopeful: The RAST test showed he's not allergic to fish which will be a nice addition to his diet.

I'm also hopeful after our visit with our NEW allergist.  She recommended doing another skin test on Little Guy since it's been 1 year since he's had one. She also thought it might help us decide on next steps along with the RAST test results.

Little Guy didn't like the skin test too much. There was definitely a lot of crying. But who wouldn't cry with little pin-pricks going into your back that may itch or hurt?  An almost 3 year old sure didn't.  I wouldn't either.

Here's Little Guy looking out the window at the allergist's office after he calmed down.  Strawberry lollipop in hand. Finally a peaceful moment!
At the allergist's office
After the food allergy skin test
The skin tests results showed: He had the biggest hives to sesame, dairy and peanuts. The secondary size hives were to almonds and walnuts, and the smallest hives were to wheat and egg.
Little Guy's skin test results - you can see the different sized hives

Next steps? The allergist recommended to food challenge wheat and egg. So, we have our wheat and egg food challenges setup on different days in May. Say some prayers for us as even adding a few more foods to his diet would open up so many more meal possibilities.

For those who are new to food allergies and may also be going through this, here's some hopefully helpful info from Dr. Robert Wood's book Food Allergies for Dummies. Here's a sample chapter.  I recommend reading it.

What is a RAST test?  
A RAST test measures the amount of allergen-specific IgE in your blood.*

What is IgE?
An antibody that your immune system releases during an overreaction to an allergenic food. The numbers you get back after your RAST test shows the level of IgE in your blood.

What is the "gold-standard" RAST test?
The most important point about RASTs is that they’re not all the same. Some types of RASTs are more accurate than others, and the results of one type of RAST are not interchangeable with the results of another type. For diagnosing food allergies, the type of RAST that has the best track record is the Pharmacia CAP fluorescent enzyme immunoassay. Wrap your mouth around that one! To simplify the nomenclature, doctors refer to this type of RAST as CAP-FEIA or CAP-RAST."*

How do I know which lab does the best RAST test?
Ask your allergist and also the lab before you go!  (this is something I didn't even know to ask). I've also learned that you should use the same lab for tests every year since RAST numbers may be different at every lab since the machines may be calibrated differently at each lab company.  Crazy!!

If you've done this before, what's your experience with RAST tests?


Unknown said...

Aww, the skin-prick test is such a pain. Keeping a 2 year old occupied and distracted from the itchy pain for an hour is hard work! And for results that (for us) aren't always accurate, too. I am not sure now what the blood test we had done is called. I know it was fairly comprehensive and measured both IgA and IgG reactions.

Kathryn @ Mamacado said...

Yes, it sure is a PAIN, you're right Jessie! I almost think the blood test is easier since it's quicker and you don't have to wait around in a doctor's office. Either way, I'm always trying to remember to give thanks that he's happy and healthy. That's all that matters, right?

Diane said...

Poor "little guy" I wish I could have been there with you Kathryn to help. I remember when Chris had to go through that but he was a bit older. I am sure glad you are so smart and aware of everything that he is allergic to and keeping updated. Can't wait to see everyone and little gal too ! :)

Kathryn @ Mamacado said...

Looking forward to seeing you too Diane!

carrie said...

How did I not know there were different types of RAST tests? I literally just took my daughter yesterday to have her yearly RAST test done and we went to a different lab! Ugh. I don't want to redo this. I hope it is ok :(

Kathryn @ Mamacado said...

I learned this tidbit from the leader of an allergy-mom group who is always full of helpful information like this! Ask your allergist though as she/he may have a different perspective about it. I'm guessing they won't say to redo it! Hope you get great results back!

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