Background: Asthma with fixed airflow obstruction (AFO) is associated with higher exacerbation rates and mortality compared to non-obstructed asthma, yet its prevalence and clinical profile remain uncertain.

Objectives: We aimed to determine the prevalence, characteristics, and comorbidities of asthma with airflow obstruction in adults ?50 years.

Methods: Participants with spirometry data from 9 CADSET cohorts (n=69,789) were cross-sectionally analyzed. In 2 asthma- and 4 COPD cohorts, AFO was defined as ever diagnosed asthma with post-BD FEV₁/FVC<0.7. In 3 population cohorts, AFO was defined as ever asthma with pre-BD FEV₁/FVC<0.7. The prevalence and co-morbidities of AFO were meta-analyzed and characteristics were compared to asthma without airflow obstruction (asthma-only) and COPD without asthma history (COPD-only).

Results: The prevalence of AFO was 2.2% (95%CI: 1.8-2.6%) in the general population, 21.0% (18.5-23.8%) in asthma cohorts and 9.9% (5.0-18.7%) in COPD cohorts. AFO patients reported significantly more dyspnea than asthma- and COPD-only. Compared to asthma-only, AFO were older, more often male, current smokers, had lower BMI, and had higher white blood cell counts, yet showed no significant difference in co-morbidities. Compared to COPD-only, AFO were younger, more often female, never smokers, had higher BMI and had more often depression (24.5 vs 11.5%, p=0.01), osteoporosis (21.8 vs 13.4%, p<0.01), and gastro-esophageal reflux disease (GERD; 36.6 vs 24.7%, p<0.01).

Conclusion: AFO is a prevalent respiratory phenotype associated with more dyspnea than asthma- and COPD-only. AFO patients had more depression, osteoporosis, and GERD compared to COPD-only.