Correspondence to: Prof. CHEN Xiang-mei, Department of Nephrology, State key Laboratory of Kidney Disease, Nephrology Institute of the Chinese People's Liberation Army, Chinese People's Liberation Army Key Laboratory of Nephrology, Chinese People's Liberation Army General Hospital, Beijing 100853, China (Tel: 86- 10-66935462. Fax: 86-10-68130297. Email: xmchen301@126.com)