1. Division of Nephrology, Department of Internal Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
2. Department of Internal Medicine, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Internal Medicine, Inje University Pusan Paik Hospital, Busan, Korea.
4. Department of Internal Medicine, The Catholic University of Korea, Seoul St Mary's Hospital, Seoul, Korea.
5. Department of Internal Medicine, Eulji General Hospital, Eulji University, Seoul, Korea.
6. Department of Internal Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.