Considering Trying a Food Allergy Challenge

Sloane Miller Health Guide
  • It's a new year and this year I feel that the time is right for me to do some food challenges.


    If you are new to my Health Central blog, you may not know that I've had food allergies my entire life. Starting in infancy, I ingested a food and had a swift and severe allergic reaction.


    Then in my 30s, I developed food intolerances to wheat, dairy and soy, which I discovered through an elimination diet over two years.

    Both the food allergies and food intolerances were discovered through direct relationships: I ate something and then had an adverse reaction.


    Several of these foods to which I am allergic or intolerant I haven't had in five, 10, 15 years or more. Needing to avoid so many foods is very restrictive and I feel like it's time to try them again and see what happens. The body changes over time, so maybe I've outgrown my melon allergy. Maybe eggplants are my new veggie friends. Or maybe everything has stayed the same. Either way I think I need to find out.

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    Kind of terrifying really.

    Why do this at all you ask? Because there is only one way to really find out where I stand with certain foods: I have to eat them.


    Why not do a blood test, a RAST or Immuno-Cap, or a skin prick test?
    The blood tests are not the most reliable in predicting causality and with the skin tests, I'm a Sensitive Sally and my test usually deliver false positives. For example, on a recent RAST blood test, I tested positive for an egg allergy. I've never been allergic to eggs a day in my life! As for skin tests, a few years back I had a hospital job and had to be screened for tuberculosis. My doctor gave me the skin test and a large wheal popped up: positive. My doctor was stumped because I've never had TB. He did a chest x-ray to make sure that I didn't have TB; naturally I came back negative. So he did another TB skin test, which also came back positive. His conclusion: I was allergic to the TB skin test! As I said, when it comes to skin tests, I'm super sensitive.


    Here's what esteemed allergist and colleague Jay M. Portnoy, M.D., has to say about this from a press release on the America College of Allergy, Asthma & Immunology site.
    In short: "Just because you have a positive test to a food doesn't mean you are allergic to the food," Dr. Portnoy said. "It is really important that the symptoms correspond to the test. Personally, I'm still seeing a lot of patients who have been told by a physician not to eat foods because of positive test results, when in fact they have never had a problem with the food. You don't want to avoid food that you are not allergic to, but you do want to avoid foods that you are allergic to. Allergists can be helpful in determining this because they have special training and experience in interpreting the test results."


    Here is what my colleague Dr. Matthew Greenhawt, a prominent Atlanta-based allergist says about allergen testing: "Both forms of testing [blood and skin prick tests] have a prominent limitation--they cannot distinguish if a positive test result really means that one has a clinical allergy to that item. In statistics, this concept is called the test's positive predictive value. Prick skin tests have been shown to only be truly positive in 30-50% of individuals tested. However, both skin and blood tests have exceptional negative predictive values, or the probability that a negative test means no allergy. Negative allergy skin tests or blood tests are >95% predictive that no allergy exists, assuming the test was performed correctly. The best test for a food allergy is an oral challenge, but this is not appropriate for everyone."


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    Yes. Bear that last quote in mind: a food challenge is not for everyone. Hardly. Depending upon the nature of your food allergy and the severity, this should not necessarily be done unsupervised or without emergency/rescue medication at hand.

    However for me, I want to test foods that are relatively low on the severity scale or at least they were ten years ago. I may do some in my doctor's office; I may do some at home with a safe person and medication at the ready. Rest assured this is a delicate undertaking.


    A food challenge can be dangerous if you do it unsupervised. If you are considering doing a food challenge to determine your food allergies, discuss all of your options and the best way to proceed for you and your family with your health care provider FIRST.


Published On: January 13, 2009