Differences in Type 2 Phenotype and Clinical Characteristics of Adult Asthma Patients with Different Severity, Across GINA Step 1 to 5 Asthma

Background: The prevalence and clinical characteristics of asthma phenotypes are less studied in mild asthma than in severe asthma. This study aims to assess the prevalence and clinical features of different phenotypes in patients with asthma with different severity. Methods: A cross-sectional study was conducted in Hong Kong. Adult patients with mild, moderate and severe asthma based on GINA steps (1 to 5) were included. The prevalence of eosinophil phenotype, elevated IgE, overlapping eosinophil phenotype with elevated IgE levels and type 2 phenotype in mild and moderate/severe asthma were compared. The clinical features of different phenotypes in patients with mild or moderate/severe asthma were also compared. Results: A total of 152 patients were recruited. The mild asthma group had significantly fewer patients with type 2 phenotype (49.0% vs 69.3%, p = 0.015), eosinophilic phenotype (25.5% vs 43.6%, p = 0.030), elevated IgE (41.2% vs 59.4%, p = 0.033), and overlapping eosinophilic phenotype with elevated IgE (17.6% vs 33.7%, p = 0.038). Those with mild eosinophilic phenotype had better lung function than their non-eosinophilic counterparts (2.67 ± 0.75 L vs 2.18 ± 0.62 L, p = 0.045), in contrast to the comparatively poorer lung function of those with eosinophilic moderate/severe asthma (87.87 ± 19.54% vs 98.10 ± 19.77%, p = 0.018). The eosinophilic phenotype and a higher blood eosinophil count were only associated with an increased risk of exacerbation in moderate/severe asthma. Conclusion: The prevalence of the type 2 phenotype is lower in patients with mild asthma than in patients with moderate/severe asthma. Eosinophilic phenotype in the mild and moderate/severe asthma group showed differences in spirometry findings and exacerbation risks. The heterogeneity in the phenotype across asthma of different severity suggests that risk stratification based on blood-based biomarkers alone may be inadequate and other clinical factors should also be considered. Keywords: asthma, clinical severity, phenotype, eosinophils