Department of Internal Medicine, Kosin University College of Medicine, Busan, South Korea. Department of Internal Medicine, Pusan National University Hospital and Biomedical Research Institute, Busan, South Korea. Department of Internal Medicine, Pusan National University Yangsan Hospital, Yangsan, South Korea. Department of Internal Medicine, Korea University Ansan Hospital, Seoul, South Korea. Department of Internal Medicine, Seoul Boramae Hospital, Seoul National University College of Medicine, Seoul, South Korea. Department of Internal Medicine, Korea University Guro Hospital, Seoul, South Korea. Department of Internal Medicine, Gachon University Gil Medical Center, Incheon, South Korea. Department of Internal Medicine, Kyung Hee University School of Medicine, Kyung Hee University Hospital at Gangdong, Seoul, South Korea. Department of Internal Medicine, Hanyang University College of Medicine, Seoul, South Korea. Department of Internal Medicine, Seoul National University Hospital, Seoul, South Korea. Department of Internal Medicine, The Catholic University of Korea Seoul St. Mary's Hospital, Seoul, South Korea. Department of Internal Medicine, Korea University Anam Hospital, Seoul, South Korea. Department of Internal Medicine, Ulsan University Hospital, Ulsan, South Korea. Department of Internal Medicine, Seoul Medical Center, Seoul, South Korea. Department of Internal Medicine, Daegu Catholic University Hospital, Daegu, South Korea. Department of Internal Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, South Korea. Department of Internal Medicine, Gangnam Severance Hospital, Seoul, South Korea. Department of Internal Medicine, Korea University Guro Hospital, Seoul, South Korea. Electronic address: parkcg@kumc.or.kr.