The allergy tests

Allergies: symptoms, treatment and sublingual immunotherapy - 4 October 2016

People are fond of tests: they seem to give an unequivocal answer. Or do they?

Certainly, the biologic reality of allergy is different from that of diabetes or pregnancy where indeed the tests are most accurate and the clinical “verdict” unescapable.

Allergy lies within the realm of biology, where proteins, large molecules which can vary in their spatial conformation, and their interactions with others make for fuzzier results. Rather than an on/off switch, the results of skin tests tell us of the presence in the patient’s skin of special antibodies called IgE, antibodies associated to allergy. But the buck does not stop there! Neither skin prick tests, intra-dermal tests or indeed serologic tests (from blood samples) can really, on their own, tell us whether a patient is allergic or not.

It should be realized that one cannot walk into an allergist’s office, show his or her arms in order to be “tested for everything.” It just does not work like that. A patient should question a physician that would proceed in this way.

The reality is that allergy tests suffer from a high rate of false positive results. Even negative tests sometimes have to be doubted. A child that has suffered anaphylaxis when eating a peanut will not be allowed to eat peanuts again simply because the skin test or the serology for that matter happens to be negative.

In serologic (blood test results), the level of IgE (often a number from 0 to 100 or a class of 0 to 6) is too often misconstrued as an indication of the severity of the reaction to be expected. Not so. This clinic has seen a young child with anaphylaxis to peanuts with an IgE level of barely 0.3…

In fact, it is what the patient tells the allergy specialist and some specifics that the allergist will ask more precisely that will often make the most difference. It is on that basis that the corroboration of positive allergy test results will help secure a diagnosis of allergy and make for a solid treatment plan.

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