Comparison of intradermal skin testing (IDST) and serum allergen-specific IgE determination in an experimental model of feline asthma.

Intradermal skin testing (IDST) and allergen-specific IgE determination are used to determine allergen sensitization. In cats, studies have found poor correlation between the two tests. However, these studies were mainly conducted in pet cats sensitized to unknown allergens with unknown dose and duration of exposure. We hypothesized that in an experimental model of allergic sensitization where these variables are controlled, IDST would demonstrate greater sensitivity and specificity than would serum allergen-specific IgE determination. A model of feline asthma employing Bermuda grass allergen (BGA) or house dust mite allergen (HDMA) was used to test the hypothesis. Thirteen cats were assigned to undergo sensitization to BGA, HDMA or saline (placebo). Bronchoalveolar lavage fluid confirmed development of an asthmatic phenotype. Serum collection and IDST were performed on D0, D28 and D50. A portion of serum was pooled, and an aliquot heat inactivated (HI) to destroy IgE. Individual, pooled, and pooled HI samples were used for allergen-specific IgE determination using an Fc epsilon R1 alpha-based ELISA; pooled samples were also analyzed using an enzymoimmunometric assay. Sensitivity (SE), specificity (SP), and positive and negative predictive values (PPV and NPV) were calculated for IDST and for BGA- and HDMA-specific IgE. Combined results for IDST found SE=90.9%, SP=86.7%, PPV=83.3%, and NPV=92.9%. For ELISA-based serum IgE testing, the SE=22.7%, SP=100%, PPV=100% and NPV=63.8%. The enzymoimmunometric assay did not detect sensitizing IgE, but did detect IgE reactivity to a variety of irrelevant allergens (even in HI samples). Sensitivity of IDST was greater than sensitivity of serum IgE measurement supporting use as a screening test for aeroallergens. Both IDST and allergen-specific IgE determination via ELISA were specific; either test can be used to guide selection of allergens for immunotherapy. The enzymoimmunometric assay was unreliable and cannot be recommended.