This study will assess the within-day variation of blood eosinophils in patients with Chronic Obstructive Pulmonary disease (COPD) in stable state and determine if there is a correlation between the blood eosinophils and certain clinical parameters.

COPD is a heterogeneous disease, resulting in different phenotypes with varying clinical and pathophysiological characteristics. One of these pathophysiological features is chronic airway inflammation which can be eosinophilic of nature. Blood eosinophils could be an accessible biomarker for this eosinophilic inflammation.

Eosinophil counts can fluctuate due to their short half-life in blood and due to a diurnal rhythm. More needs to be known about this diurnal rhythm and the different confounding factors and sources of within-subject variability of this biomarker.

Inclusion Criteria:

• Patients willing and able to give informed consent for participation in the study.
• Age 18 years or older.
• Diagnosis of COPD according to GOLD (Global Initiative for Chronic Obstructive Lung Disease): post-bronchodilator Tiffeneau index <0.7), in a stable state of the disease.
• A smoking history of >10 pack-years

Exclusion criteria:

• Clinical diagnosis of asthma.
• Use of systemic corticosteroids (oral, intravenous or infiltration) up to six weeks before inclusion.
• Pregnancy.
• A recent exacerbation of COPD (<4 weeks).

COPD patients