Distinct characteristics of asthma overlap phenotypes: Insights from the Turkish adult asthma registry

Considerable overlaps exist between asthma phenotypes and the clinical significance of these overlaps remains undetermined. The objective of this study is to analyze the characteristics of asthma overlap phenotypes using data from the Turkish Adult Asthma Registry (TAAR). This cross-sectional registry study included 2053 adult patients (74.8% female) with asthma. Overall, 39.3% (n = 697) had allergic–eosinophilic (AE), 26.0% (n = 461) had allergic–non-eosinophilic (ANE), 21.3% (n = 377) had non-allergic–eosinophilic (NAE), and 13.4% (n = 237) had non-allergic–non-eosinophilic (NANE) asthma. Severe asthma exacerbations and emergency department (ED) visits were more frequent in the AE (28.3%, 31.2%, respectively) and NAE groups (36.0%, 34.0%, respectively) than in the ANE (14.3%, 20.6%, respectively) and NANE groups (12.6%, 16.7%, respectively) (p < 0.001). FEV1 values were significantly lower in the AE group than in the ANE and NANE groups (p < 0.001, p = 0.048, respectively) and in the NAE group than in the ANE group (p < 0.001). Risk factors for poor asthma control included living in rural areas, asthma-related ED visits, FEV1 < 60% in the NAE; being overweight, chronic rhinosinusitis, oral corticosteroids use, age < 40 years in the NANE; FEV1 < 80% in the AE; and severe asthma exacerbations, ED visits for AE and ANE groups. The considerable overlap between allergic and eosinophilic asthma phenotypes has clinical implications as increased rates of asthma exacerbations and healthcare utilization. The clinical heterogeneity among asthma phenotypes based on a single biomarker highlights the importance of multidimensional asthma phenotyping.