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

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.

To estimate the proportion and assess the clinical features of asthma with low T2 markers in a general asthma population, including all severities.

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.

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.

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.