1. Department of Internal Medicine, Korea University Guro Hospital, Seoul, Korea.
2. Department of Internal Medicine, Gachon University Gil Hospital, Gachon University of Medicine and Science, Incheon, Korea.
3. Department of Internal Medicine, Korea University Anam Hospital, Korea University College of Medicine, Seoul, Korea.
4. Department of Internal Medicine, Korea University Ansan Hospital, Korea University College of Medicine, Seoul, Korea.