Saturday, November 5, 2011

In Defense of Food Allergy (IgE) Blood Tests - Part One

I feel that blood tests for food allergies are getting a pretty bad rap, lately.  I read/hear things like "they're wrong 50% of the time" and "they give a lot of false positives".  Those statements are not entirely true.

Here is an article that I read, recently:
Attention Shoppers: Free Allergy Testing In Aisle Five

It covers quite a few points, so I'd like to go through the article and express where I agree/disagree.

In the first paragraph, we find:

"I'd like to see this awareness spread to other areas of medicine where tests are widely used without strong supporting evidence.  Why not start with allergy testing?"
Right off the bat, I'm in disagreement.  I believe there is supporting evidence that blood test results can be helpful.
"Most of the children in the study had an allergy-related skin condition called atopic dermatitis, which may have made false-positive test results more likely."
Well, he is referring to skin tests, yet he lumps skin tests and blood tests together, which I don't think is fair.  My daughter had pretty bad eczema (atopic dermatitis) when she was a baby and when it came time for testing, I didn't even consider the skin-prick test.  I thought to myself, "how would they be able to tell the reactive rash from her existing rash?"  Also, even though people cringe at the thought of a blood-draw, the way I see it, it's basically one or two pokes, versus a back or arm full of pokes.  For the blood test, they can poke my daughter "once", take her blood off to a lab, and test to their heart's content, without her being present or in any more discomfort. I would imagine that it takes a little more recovery time for a skin-prick test.  Also, you can do the blood test without having to stop any medications.  For the skin prick test, it is my understanding that the patient had to stop taking their medications, like Zyrtec, Allegra, etc.  Now, I'm not trying to say the skin test is a "bad" test, but I just don't think the two should be lumped together.  

He goes on to say:

"These false diagnoses can also be very disruptive for families and their surrounding communities. Special diets are a hassle to follow and "non-allergenic" foods often cost more. Children and parents may suffer unnecessary anxiety about accidental ingestion of the wrong food. Even classmates may be affected due to the spread of "nut free zones" that restrict food choices."
Where do I start with this section?  Yes, it is disruptive to find out that your child has food allergies.  What's more disruptive is not knowing your child has food allergies and having them have an adverse reaction on a regular basis, because you have yet to identify the triggers/allergens.  It also irritates me that he would mention the "nut-free zones".  Don't we have a hard enough time convincing people of the necessity of "nut-free zones" without someone calling them into question, yet again?  (I mean, they are necessary when a child has a severe nut allergy, not just across-the-board.)  Why is it so awful to err on the side of caution, when a child's life is at stake?  Also, not all schools are "nut-free" all the time.  I know of a school that only implements those policies and precautions when a food-allergic child is actually enrolled.  If no peanut-allergic children are enrolled at the time, they return to using peanut butter for crafts, etc.  I understand that he means that misdiagnosed food allergies are a burden, but I just don't like the discouraging tone.

OK, here is something I agree with, in part:
"But his concerns about the overuse of food allergy tests are supported by the authors of recent National Institutes of Health (NIH) guidelines on food allergy, who warned that lab tests are frequently (and incorrectly) used as the sole basis for a food allergy diagnosis."
Yes, it is true that a blood test result, alone, should not usually be relied upon for food allergy diagnosis. However, sometimes, the results are so compelling, that we just have to act "as if" and assume that an allergy is present.  Who wants to find out the hard way?

Here's another part I agree with:
"A positive test does not equal a diagnosis, which is the premise of the testing programs," Wasserman said. "These tests are fundamentally useless without a formal evaluation of the patient." 
This is true, and I won't deny that.  I don't like the concept of people getting tested for allergies at the grocery store, or at the pharmacy.  The conflict of interest is staggering and the staff present are not qualified to make a diagnosis. I understand the general sentiment of the article, because I believe his main point is that we don't want people being tested across-the-board, when they've shown no signs of food allergies, because there might be false positives.

However, I see people with children who are showing signs of a reaction to something, yet they wonder if they should test, or are discouraged from testing, by their child's pediatrician.  This would not be "random" testing.  They have cause to suspect food allergies.  Yes, of course, it could be something else, but why are people so bent on discouraging the tests when there are suspicious signs and symptoms?  Even if the tests show no IgE-mediated allergies present, that is still useful information.  There are also non-IgE-mediated food allergies and food intolerances, that might be at play, but I still feel that the blood tests serve a useful purpose.  

I would like to present more information about blood tests and the usefulness of their results in Part Two, if you haven't fallen asleep, yet. ;)

1 comment:

  1. Interesting read! The original article said that there were "false positives" in that kids who showed signs of allergy when tested wouldn't notice symptoms when they actually ingested the food. He also mentions that the children in this study had atopic dermatitis. Well, I could have been one of those children. I have allergies where I know immediately when I've eaten something wrong (notably, peanuts), and I have allergies that manifest later, in sneaky, insidious ways through skin, but they are very real. Maybe there's the gut health connection or some other mechanism through which IgE allergy reactions wouldn't be immediately noticeable? I don't know. Regardless, avoiding even those allergens that I wouldn't notice if I ate them has made a big impact in my health.

    I also detest his idea that testing allergic to wheat, dairy or anything else would be a nutritional catastrophe for the child. Yes, if you have eaten wheat all your life, going wheat free would really feel like you "can't eat anything" but with proper nutritional counseling that should be offered for multi-allergic people anyway, one would find that there are plenty of things to eat in this world to fill the void. It's not that hard.