Supplementary Material for: Serum Total Immunoglobulin E Is a Surrogate of Atopy in Adult-Onset Asthma: A Longitudinal Study

Background: Studies have shown that serum total immunoglobulin E (IgE) levels are higher in asthmatics. However, the role of the serum total IgE level, independently from atopy, in adult asthma is not understood. We studied the associations between serum total IgE, the number of sensitizations and the sum of specific IgEs and new-onset asthma using longitudinal data from the European Community Respiratory Health Survey. Methods: Serum total and specific IgE to 4 common inhalant allergens were measured at baseline in 9,175 participants, with a follow-up of 9 years. Individuals with asthma history and/or asthma symptoms were excluded. Atopy was defined as the presence of at least one specific IgE ≥0.35 kU/l. Total and specific IgEs were regressed against new-onset asthma using multivariate logistic regression with a random intercept for the study centre. Results: Two hundred and ninety-seven participants had developed asthma during follow-up (incidence rate 5.7 per 1,000 person-years). A 10% higher level of total IgE was associated with a 12% increased risk of new-onset asthma (p = 0.005). However, after adjustment for the number of positive specific IgEs [odds ratio (OR) for multiple sensitization 1.74, 95% confidence interval (CI) 1.05–2.88] and the sum of allergen-specific IgEs (OR 1.18, 95% CI 1.00–1.40), the association between total IgE and asthma disappeared (OR 1.00, 95% CI 0.91–1.10). Seventeen percent of new-onset asthma cases could be attributed to atopy, and this estimate was not largely modified when the total IgE level was simultaneously taken into account. Conclusions: After taking into account the number and intensity of 4 specific IgEs, the serum total IgE level was not associated with new-onset asthma in adults.