A prospective observational study to evaluate the prevalence of severe asthma among subjects with difficult-to-treat asthma at a tertiary care center in North India

Background: Severe asthma accounts for disproportionate asthma-related morbidity, mortality, and healthcare costs, yet prospective data on its prevalence remain limited, particularly for developing countries. We aimed to determine the prevalence of severe asthma among subjects with difficult-to-treat asthma at a tertiary care center in North India. Methods: Between January and December 2023, we prospectively enrolled consecutive adults with difficult-to-treat asthma that remained uncontrolled despite treatment with medium- or high-dose inhaled corticosteroids-long-acting beta-agonist (ICS-LABA) or required high-dose ICS-LABA to maintain good control. All subjects underwent systematic evaluation, including diagnosis confirmation, assessment of inhaler technique and adherence, comorbidity screening, and treatment optimization, with reassessment after 3–6 months. We diagnosed severe asthma (uncontrolled despite high-dose ICS-LABA or required high-dose ICS-LABA to maintain good control) after addressing all modifiable factors and assessed type 2 (T2)-targeted biological therapy eligibility. Results: Among 240 subjects (mean age 47.4 ± 14.9 years; 68.8% female), we identified modifiable factors in 218 (90.8%), including suboptimal therapy (74.2%), poor adherence (64.2%), and incorrect technique (58.8%). Following interventions, 154 completed reassessment; 102 (66.2%) no longer met severe asthma criteria. Overall, 67 subjects had severe asthma (27.9%; 95% CI: 22.4-33.9%). Among them, 66.7% had blood eosinophils ≥150 cells/µL, and 68.7% met criteria for T2-targeted biological therapy. Conclusion: Approximately one-quarter of subjects with difficult-to-treat asthma have confirmed severe asthma after systematic assessment. A significant proportion improve with targeted interventions, emphasizing the importance of comprehensive evaluation. Most patients with confirmed severe asthma are candidates for T2-targeted biologicals, highlighting the need for structured assessment protocols and improved access to biological therapies.