3.1 A Most Interesting Conundrum

“I’m allergic to (insert noun here—life, the State of Missouri, etc).” Anyone who practices allergy for even a short period of time will come across some difficult situations that can cause practitioner and/or patient frustration. One of these scenarios is the patient with numerous positive allergy tests, regardless of whether it is skin or blood testing. Oddly, patients in this scenario tend to react in one of two main ways—the first reaction being an acceptance that they are truly “allergic” to everything, consigned to atopic doom, and that you must absolutely treat them with everything for which they have positive tests. But, are they truly “allergic” to everything?

The second way a patient found to have numerous positives can react, “Your tests must be wrong, Doc/I don’t understand—I’ve been exposed to (insert noun here—cats, dust, the summer season, etc.) and don’t have any problems.” Without proper explanation, this can lead to patient confusion, misunderstanding (a false acceptance of allergy when there is none), or mistrust of the testing process or the practitioner (“I’m not allergic to my dog, this quack has no idea how to do this”). Without proper understanding on the practitioner’s part, this can lead to overtreatment, unnecessary avoidance, and lack of perceived treatment benefit.

3.2 Serious Stuff

What is sensitization? In this case, sensitization is the demonstration of immunoglobulin E (IgE) antibodies to one or more antigens. The type of testing (skin vs. blood) is irrelevant, because if the patient is sensitized, there will be one or more positive allergy tests. The key here is that sensitization does not equal symptoms. It is important to understand that sensitization is not same as having clinical symptoms.

What is allergy? In this case, allergy is the correlation of clinical symptoms (i.e., sneezing, itching, etc.) with exposure to an antigen plus a positive allergy test result (skin or blood), indicating the presence of IgE antibodies to that particular antigen. For example, a patient with a positive skin test result to cat has nasal congestion when exposed to cats. This is allergy.

So you’re saying my patient who had positive test results (skin or blood) for dust mites but has no symptoms on exposure to dust isn’t allergic to dust mites? Technically, yes. This is an example of sensitization without clinical allergy. While the patient demonstrates IgE to dust mites, there’s no correlation to clinical symptoms.

But, the test results were super positive! Huge wheals on skin testing (or massive levels of IgE)! They MUST be allergic! No. This is one of the frustrating things about allergy. The actual level of sensitization does not necessarily correlate with the severity or presence of allergy symptoms. A patient with barely positive allergy test results may have serious or life-threatening reactions on exposure; on the contrary, a patient with markedly positive test results may have very mild, barely troublesome symptoms. The presence of a positive test result by itself indicates sensitization, not allergy.

Why does this happen? Well, we’re not completely sure. Some of this is due to the cross-reactivity of different antigens and the sharing of epitopes at a molecular level. There are some recent data suggesting that it’s not just the presence of IgE that is important, but the ratio of IgE to IgG (or more specifically IgG4) that may help distinguish patients with sensitization only from those with clinical allergy. However, there’s not enough evidence at this point to recommend ordering antigen-specific IgG4 routinely.

What if the patient forgot she/he has symptoms? This happens. Allergy patients are notorious for thinking their symptoms are “normal.” There are a number of patients who have told the author with a straight face that “normal people can’t breathe out of their nose.” Particularly for patients with year-round allergies, these symptoms tend to become their “normal” and they may not report them to you or view them as significant. It’s something they’ve lived with for so long, it’s just become the way things are for them. However, after testing, once attention has been drawn to certain antigens, patients will sometimes put two and two together and figure out after the fact that they really do have problems with that particular antigen.

So, if the patient wants immunotherapy, what do I treat for? Allergy is a history of symptoms on exposure with a positive test result, so only treat for antigens that meet this definition. It is not recommended that the patient should be treated for antigens that only demonstrate sensitization.

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