Ragweed skin test responsiveness correlates with specific immunoglobulin E levels

Evaluation for allergic rhinitis requires an objective measure of atopy. Serum eosinophils, total and specific immunoglobulin E (IgE), and skin testing have been used as this measure. The objective of our study was to examine the relationship between in vitro allergy tests and in vivo responsiveness. We compared eosinophil counts, total IgE, and the specific IgE radioallergosorbent test (RAST) measurements to end point skin test titrations with ragweed. Forty subjects ≥18 years of age with at least a 2-year history of moderate to severe ragweed-allergic rhinitis and a positive skin-prick test to ragweed participated in this study with 33 subjects having data for all measurements. End point skin tests were performed by intradermal injection of 0.03 mL of threefold dilutions of standardized short ragweed extract into the forearm. Ragweed-specific IgE was significantly correlated to end point wheal and erythema concentrations. The results were similar whether the end point wheal (r = -0.714; p < 0.001) or erythema (r = -0.862; p < 0.001) concentration was used, and the correlation between these two values was significant (r = 0.97; p < 0.001). However, 8 of 33 subjects had a negative specific IgE RAST value for ragweed. There was a significant relationship between ragweed-specific IgE and total IgE (r = 0.72; p < 0.01). No significant correlations were found between blood eosinophils and either total IgE, ragweed-specific IgE, and end point wheal or erythema concentrations. Skin test responsiveness to ragweed correlated with in vitro ragweed-specific IgE levels, but these tests are not equivalent indicators of the degree of IgE-mediated sensitivity.