Supplementary Material for: Allergy in young adults associates with elevated FeNO levels and IgE-verified parental allergy but is confounded by self-reported symptoms

Introduction: Knowledge of IgE-verified allergy in young adults is limited as most studies are based on self-reported data. Allergic heredity is important in allergy development in early life, but less is known about the hereditary component later in life. The aim was to investigate IgE-verified and self-reported allergy and asthma at 20 years of age in association to parental allergy and environmental factors. Methods: In total, 281 individuals born into the cohort of parents well-characterized regarding allergic disease were followed to 20 years of age. The participants were categorized by parental allergy and examined regarding allergic diseases (IgE-sensitization and allergic symptoms) at 2, 5, 10 and 20 years of age. FeNO was measured at 10 and 20 years. Results: In total, 45% of the study participants were allergic, with twice as many self-reported cases at age 20. Rhinitis was key to distinguishing confirmed allergy from self-reported. Having two allergic parents and increased FeNO were associated with an increased prevalence of allergic disease at 20 years. From a longitudinal perspective, rhinitis increased from childhood to young adult, in all heredity groups. Conclusion: In this longitudinal study we have shown that two allergic parents as well as increased FeNO levels seem to be of importance for being allergic at twenty years old. Self-reported allergy was over-reported - a result that should be considered in future survey-based reports on allergic diseases.