FC‐53 Serologic allergy testing in horses with insect hypersensitivity

Abstract

Serologic allergy testing (SAT) results in horses have not been consistent with manifestations of hypersensitivity or intradermal test (IDT) results. The purpose of this study was to determine whether the level of agreement between insect‐specific IgE values (as measured by a commercial polyclonal antihorse IgE‐based ELISA) and manifestation of disease or IDT was improved by shifting the positive/negative threshold from 200 (positive) to 150 (borderline) or by the utilization of insect type‐specific cut‐off points. The study included a population of 37 healthy horses and 40 Icelandic horses suffering from insect hypersensitivity. The study was conducted during the fall when affected horses showed acute clinical signs. IDT was performed as standard procedure using extracts of black ant, mosquito, horsefly, deerfly, housefly, and Culicoidesvariipennis. Insect‐specific IgE levels in horse sera were measured by an equine ELISA. Sensitivity and specificity was 98 and 3% (SAT versus insect hypersensitivity) and 97 and 4% (SAT versus IDT), respectively. A shift of the threshold value from 200 to 150 increased sensitivity, but did not improve the level of agreement between IDT and SAT (κ = 0.04, slight agreement). Circulating allergen‐specific IgE levels were not significantly different for the incidence and size of positive skin reactions or the onset and severity of insect hypersensitivity for any insect tested. Therefore, the utilisation of insect type‐specific cut‐off points did not increase the level of agreement between SAT and IDT or clinical data. Funding: Self‐funded.