Testing, Testing . . . Atopy in Dogs
Atopic dermatitis is a common allergic skin disease of dogs. The diagnosis is primarily clinical on the basis of compatible clinical signs and ruling out other common causes of pruritus. In some patients, immunotherapy is the treatment of choice. Allergen-specific immunotherapy is based on intradermal (IDTs) or serologic tests (STs) that identify allergen-specific IgE hypersensitivities. In this study, the authors evaluated a commonly used point-of-care immunodot assay (Allercept E-Screen-Heska, Fort Collins, CO) to predict the results of an IDT or ST. All three tests were performed on 30 dogs with atopic dermatitis. The Allercept E-Screen uses canine IgE as a positive control and a test dot consisting of fleas, house dust mites, and pollens. In this study, Allercept E-Screen agreed with IDT in 26 of 30 dogs (87%) and with ST in 25 of 30 dogs (83%). The calculated probabilities for obtaining a positive IDT or ST were 70% and 67%, respectively. If IDT or ST was performed only in dogs with a positive E-Screen test, the probability of predicting a positive test increased from 70% to 95% and from 67% to 90%, respectively.
COMMENTARY: Once it is decided that allergen-specific immunotherapy is needed for a dog, the next question is, "When is the best time to test the dog?" Based on the findings in this study, it seems reasonable to use the E-Screen as a "gate keeping" test for advanced allergy testing. If you limit testing to dogs with only positive E-Screens, there is at least a 90% probability that either the IDT or HESKA full screen (Allercept ASIS) will identify positive allergens. It is important to note that E-Screen may be predictive of other commercial serologic tests as well. The next most obvious question is, "What should be done with a clearly allergic dog that is E-Screen negative?" For these dogs, I would recommend a food trial and/or medical management, pending rescreening in 2 to 3 months.
Evaluation of a point of care immunodot assay for predicting results of allergen specific intradermal and immunoglobulin E serological tests. Olivry T, Jackson HA, Murphy KM, et al. VET DERMATOL16:117-120, 2005.