Discrepancies in the bilateral intradermal test and serum tests in atopic horses

We continue to not recommend systemic allergy testing as there continues to be little support for their accuracy. If used remember this caution you see repeatedly in research papers: “test results should be interpreted with great care”. For more on the diagnosis of itchy skin see the article.
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Discrepancies in the bilateral intradermal test and serum tests in atopic horses
Vet Dermatol. 2020 Aug 3.
Catharina M M van Damme 1 , Jan van den Broek 2 , Marianne M Sloet van Oldruitenborgh-Oosterbaan 3

Affiliations
1 Department Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 108, Utrecht NL, 3584 CM, The Netherlands.
2 Department Population Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, Utrecht NL, 3584 CM, The Netherlands.
3 Department Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112, Utrecht NL, 3584 CM, The Netherlands.

Abstract
Background: In equine atopic patients intradermal testing (IDT) and immunoglobulin (Ig)E serology are used frequently. There is little evidence regarding the reproducibility of the IDT and IgE serology in horses.

Objectives: To compare the results of a simultaneously performed IDT on the left and right side of the neck in atopic horses, and to compare these results with allergen-specific IgE serology.

Animals: Ten equine patients from a university hospital population with chronic urticaria and/or pruritus.

Methods and materials: The IDT was performed using 16 allergens and the results were evaluated after 30 min, 1, 4 and 24 h. Thirteen allergens also were analysed in duplicate with two monoclonal allergen-specific IgE enzyme-linked immunosorbent assays (ELISA).

Results: Good agreement (Kappa > 0.6) between left and right IDT was found only for Dermatophagoides farinae, Lepidoglyphus destructor, birch pollen mixture and perennial rye at 30 min, birch pollen mixture at 1 h, and Acarus siro and nettle and common mugwort mixture at 4 h. The bilateral comparison of the other allergens and even the same allergens at other time points showed little or no concordance between left and right IDT. The interlaboratory comparison between both ELISAs, and the comparison between the ELISAs and IDT, showed a good agreement for two of 13 allergens: D. farinae and Dermatophagoides pteronyssinus.

Conclusions and clinical importance: Based on these preliminary data, IDT and IgE serological test results should be interpreted with great care and further studies are needed to indicate the clinical relevance of these findings.