1. Department of Laboratory Medicine, College of Medicine, Kangwon National University, Chuncheon, Korea.
2. Division of Pulmonary, Sleep and Critical Care Medicine, Department of Internal Medicine, Korea University Ansan Hospital, Ansan, Korea.
3. College of Nursing, Korea University, Seoul, Korea.
4. Division of Respiratory and Critical Care Medicine, Department of Internal Medicine, Korea University Anam Hospital, Seoul, Korea.
5. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Korea University Guro Hospital, Seoul, Korea.