Characteristics of Adult Asthma Based on Type 2 Inflammation Markers: A Population-Based Study

Background: The “type 2 (T2)-high” phenotype has a relatively well-defined pathophysiology compared with “T2-low” asthma. T2-low asthma has been mostly studied among severe asthma cases. Objective: To estimate the proportion and assess the clinical features of asthma with low T2 markers in a general asthma population, including all severities. Methods: Participants with current asthma from the population-based adult West Sweden Asthma Study were included. High T2 markers were defined as the blood eosinophil count ≥0.15 × 10⁹/L or fractional exhaled nitric oxide ≥20 parts per billion or asthma being allergen driven. If none of these were present, the case was considered as asthma with low T2 markers. Results: In total, 896 participants were included, of whom 14.3% had low T2 markers. The low T2 marker group had female predominance and had later asthma-onset age compared with the high T2 marker group. Participants with low T2 markers had better spirometry results in terms of airflow obstruction parameters but had more asthma-related emergency visits in the past 12 months than those with asthma with high T2 markers. Conclusions: In a general adult asthma population, 1 in 7 individuals have low T2 markers according to the criteria used in this study. Importantly, these individuals had better lung function than individuals with high T2 markers but a significantly increased risk of asthma exacerbations. Thus, having asthma with low T2 markers is an independent risk factor for exacerbations, which should be considered when assessing patients with asthma clinically.