LIU Dong-wei and Wan Jia contributed equally to this study. Correspondence to: Dr. LIU Zhang-suo, Department of Nephrology, The First Affiliated Hospital, Zhengzhou University; Institute ofNephrology, Zhengzhou University, Zhengzhou, Henan 450052, China (Tel and Fax: 86-371-66862901. Email: zhangsuoliu@sina.com)