Agreement of serum allergen test results with unblocked and blocked IgE against cross-reactive carbohydrate determinants (CCD) and intradermal test results in atopic dogs

Background Tests for allergen-specific immunoglobulin E (IgE) are used to select allergens for immunotherapy in atopic dogs. Antibodies against cross-reactive carbohydrate determinants (anti-CCD IgE) have been identified in serum samples of atopic dogs. Their presence in humans is a known cause of clinically irrelevant polysensitization to plant allergens. Objectives To compare the results of an intradermal test (IDT) and a serum test for allergen-specific IgE, with and without blocking anti-CCD IgE, before testing in dogs. Animals Thirty-one privately owned dogs with atopic dermatitis. Methods and materials Dogs were prospectively skin tested and their serum samples were analysed for anti-CCD IgE. An Fc-epsilon receptor-based serum test for allergen-specific IgE was performed with and without blocking anti-CCD IgE. Results In dogs with negative anti-CCD IgE samples, the agreement between the results of the serum test and the IDT was substantial (kappa = 0.71). Dogs with positive anti-CCD IgE samples (38.7%) showed no agreement between serum and skin testing (kappa = -0.35), blocking anti-CCD IgE in those samples resulted in a fair agreement (kappa = 0.43). Anti-CCD IgE positive sera had multiple positive results for grass and weed allergens, and blocking decreased them markedly. Conclusion and clinical importance Intradermal testing agreed best with serum testing in dogs with no detectable anti-CCD IgE. Sera containing anti-CCD IgE had no agreement with IDT. Test agreement was improved by blocking the anti-CCD IgE. Apparent serum test polysensitization to plant allergens was associated with anti-CCD IgE.