Methodologic aspects of the quantification of skin prick test responses: The EGEA study

Abstract

Background: The expression of responses of allergy skin prick tests is not standardized. Usual definitions of atopy are not quantitative. Objective: We sought to perform a biometric analysis of responses to various allergens to propose synthetic, quantitative indices independent of the heterogeneity of responses to various allergens. Methods: Adults (N = 1286) from the Epidemiological Study on the Genetics and Environment of Asthma, Bronchial Hyperresponsiveness, and Atopy (EGEA) were included in the analysis. The first step, conducted for 678 subjects with at least 1 wheal >0, was to perform a standardization of wheal diameters to obtain comparable figures for 10 allergens through use of the means of the squares of wheal size as a scaling factor. The second step was a factor analysis of the standardized responses conducted not only for all subjects but also separately for asthmatic case and nonasthmatic control subjects. Finally, the strength of the link between various dichotomous and quantitative scores was assessed with multiRAST, total IgE, and asthma. Analyzed quantitative scores were based on the number of positive responses and on the nonstandardized and standardized sizes of the wheals. Results: The standardization was efficient. Among asthmatic subjects but not other subjects, factor analysis evidenced a pattern with 3 factors, corresponding to outdoor, indoor, and mold allergens. The link study showed that all scores performed very similarly. Conclusion: The number of positive tests is a quantitative score with valid biometric properties. It should be used more widely in clinical settings and in epidemiology to assess the severity of atopy.