Do you wonder about the specificity of allergen-specific IgE tests in dogs (the percentage of dogs not allergic to an allergen that are correctly identified as non-allergic)? Hopefully, you are using clinical criteria to make the diagnosis of canine atopic dermatitis (CAD), not serum allergy test results. Addressing this issue definitively is not as simple as it may seem, since there is no true gold standard to determine allergen-specific sensitivity.
Several studies have reported results, however, that should give you a healthy skepticism about the specificity of serum allergy tests, even when considering the tests for the sole purpose of selecting allergens for immunotherapy, if not for diagnosing CAD. These false positive results may occur due to non-specific binding in assays or cut-off values that are set too low.
Codner submitted serum samples from five normal greyhound dogs (http://www.vetrespit.com/resources/codner.pdf). Four of the five dogs had multiple highly positive reactions.
In a recent report, 18 non-atopic West Highland White Terrier dogs were allergy tested. Multiple highly positive reactions were reported by the laboratory for 45 of the 48 allergens tested with the Allercept® test, leading the authors to conclude that the test was not specific for this population of dogs.
Today, at the World Congress of Veterinary Dermatology in Vancouver, there was a nice presentation describing why horseradish peroxidase conjugated monoclonal IgE antibody should not be used in assays, due to the high level of non-specific binding which results with certain allergens. Some laboratories disclose the conjugate that they use in their assays, but others do not.
The bottom line: do not use allergy test results to make a diagnosis of atopic dermatitis and don’t rely upon them exclusively for allergen selection for immunotherapy.