This study aims to evaluate how airway inflammation, lung function, and symptoms change over time in people with chronic obstructive pulmonary disease (COPD). Airway inflammation will be assessed using a simple breath test (FeNO) and a small blood sample to measure eosinophils, a type of white blood cell. Participants will be followed for one year, with three study visits (at the start, 6 months, and 12 months). The goal is to understand how these markers evolve and whether they differ between people who experience a worsening of symptoms (called exacerbations) and those who remain stable. All tests except for a small extra blood draw are part of routine COPD care. Participation does not affect standard treatment.

Inclusion Criteria:

• Adults aged ≥ 40 years
• Diagnosed with COPD according to GOLD criteria
• Attending routine follow-up visits every 6 months
• Ability to provide informed consent

Exclusion Criteria:

• Recent respiratory tract infection or exacerbation (either moderate or se-vere) (<4 weeks before inclusion)
• Dominant asthmatic phenotype (ACO with asthma predominance)
• Severe comorbidities interfering with participation or follow-up