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 screenFormal 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!