Evaluation of a rapid, qualitative, allergen‐specific IgE screening immunoassay as an aid in the diagnosis of atopic dermatitis in dogs

Abstract

An inexpensive, rapid, in‐clinic IgE screening immunoassay [Allercept™ E‐Screen™– (E‐Screen)] has been developed to detect the presence of aeroallergen‐specific IgE in the serum of potentially atopic dogs. The working hypothesis of this study is that a positive E‐Screen result is an effective indicator of the likelihood of positive results on a 48‐aeroallergen‐specific IgE immunoassay [Allercept™ Northeast Regional Allergy Screen – (ANRAS)] and 45‐aeroallergen intradermal testing (IDT) in dogs with atopic dermatitis. The objective of this study was to compare the results of the E‐Screen to the results of the ANRAS and IDT in dogs with atopic dermatitis. Forty‐four dogs with a history suggestive of atopic dermatitis were included in the study. The diagnosis of atopic dermatitis was based on history, physical findings, and systematic rule out of other causes of a primary pruritic skin disease. This included the use of home‐cooked elimination diets for 8‐week trials and empirical treatment for scabies when appropriate. Dogs with a concurrent flea allergy dermatitis or cutaneous adverse reaction to foods were excluded. All clients of the dogs in the study complied with the following drug withdrawals prior to testing: 90 days for all repositol corticosteroids; 30 days for all other injectable, oral and topical corticosteroids; 14 days for all antihistamines, antibiotics, antifungals and essential fatty acid supplements; and 7 days for all nonsteroidal anti‐inflammatory drugs. For each dog included in the study, the E‐Screen, ANRAS, and IDT were performed. All investigators involved were blinded as to the results of the E‐Screen until the end of the study. Only dogs with IDT and ANRAS results compatible with the dog's history of pruritus were considered for further evaluation. These dogs were subsequently treated using allergen‐specific immunotherapy (ASIT) utilizing the results of IDT alone for selection of allergens and followed for a minimum of 6 months. The results of IDT and ANRAS were compatible with the history of pruritus in 30 dogs, with the E‐Screen test being negative in 17 dogs (57%) and positive in 13 dogs (43%). Follow up on ASIT was obtained on all 30 dogs, with a range of follow up of 6–22 months (mean 13.3 months). Seventeen owners reported a >50% reduction in pruritus with ASIT alone. Four owners reported mild adverse reactions, and the ASIT injection protocols were modified with a >50% reduction in pruritus being reported with ASIT alone. Two owners reported <50% reduction in pruritus with ASIT alone, and seven owners reported severe adverse reactions such that ASIT was discontinued. These observations strongly support the likelihood that the allergens used in ASIT are significant causes of the dogs’ atopic dermatitis. Due to the high numbers of false‐negative E‐Screen test results (57%), it is not recommended that this test be used to screen for the presence of aeroallergen‐specific IgE in the serum of potentially atopic dogs. Funding: Heska Corporation.