Intradermal reactivity to two concentrations of pollen extracts in atopic dogs

Intradermal test (IDT) is used widely for determination of allergens to include in allergen-specific immunotherapy (AIT). The optimal concentration of allergen solutions used for testing has not been established in atopic dogs. Inadequate concentrations could lead to falsely negative test results and lack of inclusion of important allergens in AIT.

To compare IDT reactivity to two concentrations of five pollen extracts and determine the effect on ASIT prescription.

Atopic dogs (n = 67) had IDT results including all of the allergens of interest.

Medical records from a veterinary teaching hospital were reviewed for all atopic dogs undergoing IDT over a three year period. In addition to the hospital's standard IDT concentration of 1,000 PNU/mL for pollen allergens, five pollen allergens of higher concentration (3,000-8,000 PNU/mL) had been added at the beginning of that period. The IDT scores for the standard test concentration of each of the five allergens were compared to the scores for the higher concentration.

Positive reactions occurred much more commonly to the higher test concentration for each of the paired allergens (P < 0.05, chi-square). The AIT formulation was different in 58% of the dogs from what it would have been without the higher concentration allergens.

The current standard IDT concentration of 1,000 PNU/mL for pollen allergens is likely too low, possibly resulting in inaccurate AIT formulations. This might explain treatment failures and the incorrect diagnosis of atopic-like dermatitis. Further work is needed to establish optimal allergen test concentrations.