Comparison of immediate intradermal test reactivity with serum IgE quantitation by use of a radioallergosorbent test and two ELISA in horses with and without atopy.

OBJECTIVE: To compare a radioallergosorbent test and 2 ELISA with intradermal testing for the determination of environmental allergen hypersensitivity in horses with and without atopic diseases.
DESIGN: Prospective clinical study. ANIMALS: 10 horses with recurrent urticaria, 7 with atopic dermatitis, 16 with chronic obstructive pulmonary disease, and 22 without atopy. PROCEDURE: History, physical examination, hemogram, serum biochemical analyses, bronchoalveolar lavage, and an intradermal test (used as the criterion standard) with a regional panel of 73 allergens were performed in all horses. Serum was analyzed by use of the 3 in vitro assays of allergen-specific IgE.
RESULTS: An ELISA based on the alpha chain of the high-affinity IgE receptor, the Fcepsilon receptor immunoglobin epsilon chain (FcepsilonRIalpha) for IgE, had the overall highest kappa statistic (0.238), positive predictive value (49%), and negative predictive value (78%). Overall agreement between the FcepsilonRIalpha-based ELISA and the intradermal test was fair. The highest kappa statistic was obtained by the FcepsilonRIalpha-based ELISA in horses with atopic dermatitis (0.330). Kappa statistics for the radioallergosorbent test and a polyclonal antibody-based ELISA agreed slightly with that of the intradermal test at best. CONCLUSIONS AND CLINICAL RELEVANCE: None of the 3 serum allergy tests reliably detected allergen hypersensitivity, compared with the intradermal test. The FcepsilonRIalpha-based ELISA performed significantly better overall than the other 2 tests. Low sensitivity of all 3 assays indicates the need for continued study to elucidate a more sensitive test for the determination of potentially pathogenic allergens in horses.