The Significance of a Class I Allergy Blood Test Result

My wheat allergy blood test was a Class I result, which means it was a low positive. My doctor had the following to say about my result.

“Wheat testing at level that is unlikely to be clinically significant. More likely this is a false positive test result.”

I really don’t understand the meaning of “false positive” in this context. The only definition I could find for “false positive” online is when the test is positive, but the subject being tested does not react to the substance in question. I’m sure in many cases, a food challenge is used to determine whether or not a person reacts to a given food. My doctor didn’t suggest it in my case because of my gluten sensitivity. However, I believe I have a strong history of reactions to wheat, gluten, or maybe both. I’ve been struggling with cross-contamination and exposure to trace amounts now for nearly three years. I’ve come to react to very low traces, like what was left behind on my keyboard, mouse, and lunchbox even after wiping them all down with disposable wipes and residue left on refrigerator shelves from  grocery store packages.  I was dealing with these issues long before I completely eliminated guar gum and vinegar. My symptoms after ingesting flaxseed are quite different from the ones I’ve been getting from cross-contamination and trace exposure, and I’ve not noticed those symptoms for years now. Also, cutting wheat alone made such a huge difference in my symptoms and how I felt in a very short time, in a matter of days. Even after the first day I had already noticed some pretty big differences. Also, my wheat IgE blood test was positive while the one for gluten was most definitely negative. Wheat is what I suspect the most.  If gluten is an issue, it would more likely be from celiac disease or gluten sensitivity.  Antihistamines wouldn’t help in either of these cases.  Gluten allergy is actually pretty rare from what I understand.

When the nurse who called me about my results gave me the explanation for the “false positive” from the doctor, she said that when the results are too low to be clinically significant, they’ll label them as falsely positive. Perhaps this varies depending on the food being tested. I’d read where wheat usually has to have a higher result than some other foods before it might be considered clinically significant. That might be why my result, which is a clear Class I rather than just barely out of the Class 0 range, which is what I was expecting, is not considered clinically significant. However, I think this ignores or brushes away my clear and convincing history, which is years long now, of possible reactions to wheat. It’s very possible that a food challenge may be the only way to know for sure, but I’m not sure if a gluten-free medium like wheat starch could be used. I don’t want to do a food challenge except as an absolute last resort, but I plan to ask about wheat starch if it does come up with a different allergist. The possibility of celiac disease is just too great for me to want to take a chance with gluten ingestion.

I decided to see what information I could find online concerning Class I results, what they mean and how they can be interpreted. Here are some of my findings. Emphasis is mine where included.

• The results of an allergy blood test only indicate the likelihood of a reaction. They don’t help predict the symptoms of a reaction or how severe they will be.

  • From “What You Need to Know About Food Allergy Testing”: “Individuals with higher blood (or skin) tests are at no more increased risk of anaphylaxis than someone with minimally positive tests.”

  • The article on the above page even goes on to conclude that “class levels are meaningless”.

• If a person doesn’t react to a food or can eat the food with no problems, then any positive test result, even a high positive, may be construed as a false positive result. As stated above, this was the only definition of “false positive” that I could find online.

• It is possible to be allergic to a substance for which you scored a Class I or a low positive, and it’s even possible to have severe reactions.

  • From Riley Hospital for Children’s Allergy Testing information page: “a child might have a low score on the test, but experience anaphylactic shock in reaction to the allergen”

  • From a discussion in the BabyCenter Community: “You could have a level 1 allergy but an anaphylactic reaction …”

  • A co-worker whose daughter has a soy allergy said that her daughter scored a low positive on the soy allergy blood test.

• Even those with negative or undetectable levels of IgE in the test may still react to the food in a food challenge.

• From the Mayo Medical Laboratories Interpretive Handbook, which is actually discussing the wheat IgE test specifically: “Detection of IgE antibodies in serum (Class 1 or greater) indicates an increased likelihood of allergic disease as opposed to other etiologies and defines the allergens that may be responsible for eliciting signs and symptoms.”

• From Blood Testing for Allergies at Everyday Health: “If your test results come back positive for an allergen, you are almost definitely allergic to that substance. If your results come back negative, however, your doctor may recommend further testing, since there is a small chance of false negative results when it comes to allergy blood testing. A false negative result says you are not allergic to something when you actually are.”  This discussion revolves around testing for foods that are already highly suspected of being reactive.  In my case, I highly suspect reactions to wheat.  My positive blood test could then indicate an allergy to wheat.

• From Food Allergy Research and Education: “Despite the high chance that the blood test or skin test may be positive despite there being no allergy, or, rarely, negative despite there being allergy, in the hands of an experienced allergist, blood and skin tests are extremely helpful. This is especially true when the results are interpreted in the context of your medical history. For example, if your history suggests that you have had several reactions after eating soy products, and the blood tests show a positive reaction to soy proteins, it is very likely that you do have a soy allergy. Your allergist may order additional tests, if necessary.”

• From Interpreting RAST (Blood Test) Results for Food Allergies: “Wheat RAST greater than 26 KU/L) indicates a 74% chance one will react when eating wheat. Wheat is often positive at low levels in people who are allergic to grass pollen and may not cause reactions in that situation.”  I still think the discussion of false positive results seems to revolve around the fact that the person being tested does not react to the food in question. I also may be allergic to grass pollen. If I don’t wear a mask while cutting grass, I can get some nasty symptoms. However, this is not the time of year for me to be getting those symptoms. Pollen allergy time for me is usually in the early spring. The antihistamines have to be helping with something else, and I have not been having nasal symptoms, which I get during pollen season.

I believe pretty strongly at this point in time that I have a wheat allergy. It may be on top of or instead of celiac disease or non-celiac gluten sensitivity. At the very least, I believe I’m having some kind of food allergy reaction because symptoms I get after eating improve after I take an antihistamine.  I’m hoping that another allergist can give me a different opinion on my history and results. At the very least I’m hoping he will see enough cause to give me an epi-pen prescription in case I ever need an epi-pen to stop a serious reaction in the future. Also, if you’re searching or have questions about your low positive allergy test result, I hope the findings compiled here can help answer your questions. I thought it would be helpful to put the things I’d found on various sites and through various searches in one place.

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