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For Allergy Testing, the Art is in Interpretation

Clinician's Brief (Capsule)

Dermatology

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April 2014

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Allergen-specific immunotherapy (ASIT; injection or drops) is a common treatment modality for canine atopic dermatitis with therapy recommendations based on in vivo (intradermal), in vitro (serum allergen), or a combination testing. Sera from 10 dogs diagnosed with atopic dermatitis were collected; samples were divided into 4 equal aliquots with each aliquot submitted to 1 of 4 commercial laboratories for allergen-specific IgE assay. Although the testing methodology was similar (ELISA), each testing protocol differed with binding of canine IgE in their assays. The overall diagnostic agreement across all dogs and laboratories was slight when corrected for chance. The diagnostic agreement by dog and laboratory pair was also slight for most comparisons. There was slight agreement for plants and fungi, but substantial agreement for mites. Regarding allergen-
specific therapy recommendations, the overall agreement between laboratories was slight.

Global Commentary

The lack of agreement among the laboratories found in this study was not unexpected. Diagnostic methodologies are not standardized; however, they are not standardized for intradermal skin testing either. Standardization of in vitro and in vivo allergy testing is important as these tests are used worldwide, and the lack of standardization makes it difficult to compare data from global studies. This creates difficulty in making evidence-based medical recommendations.

Of note, this was a small study (n = 10 dogs), and testing a larger group may show different results. What really needs to be evaluated is the response of patients to immunotherapy based on the information provided by these laboratories. However, there is a major caveat: Results from allergy tests (in vitro or in vivo) reflect exposure, and it is the clinician’s responsibility to determine if these are relevant. The only way this can be determined is by asking the client when the dog is itchy and during which season itching is worse. Clients should be reminded that it may take 6–12 months to see maximum benefit; some patients respond better to one form of ASIT; and some patients need their ASIT to be reformulated. The test results are just a tool, and ASIT formulation is the art of practice.—Karen A. Moriello, DVM, DACVD

Source

Agreement between allergen-specific IgE assays and ensuing immunotherapy recommendations from four commercial laboratories in the USA. Plant JD, Neradelik MB, Polissar NL, et al. J VET DERMATOL 25:15-e6, 2014.

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