1. Department of Pulmonary Medicine, Länsi-Pohja Central Hospital, Kemi, Finland
2. Department of Pulmonary Medicine, Päijät-Häme Central Hospital, Lahti, FI-15850, Finland
3. Department of Medicine, Laboratory Department, University Hospital, Helsinki, Finland
4. Departments of Clinical Physiology and Nuclear Medicine, Laboratory Department, University Hospital, Helsinki, Finland
5. Respiratory Epidemiology, National Institute for Working Life, Stockholm, Sweden
6. The OLIN Studies, Department of Medicine, Sunderby Central Hospital of Norrbotten, Luleå, Sweden