1. College of Medicine, Southwest Jiaotong University, Chengdu, Sichuan 610031, P.R. China
2. Department of Gastroenterology, Chengdu First People's Hospital, Chengdu, Sichuan 610016, P.R. China
3. Central Laboratory, General Hospital of Western Theater Command, Chengdu, Sichuan 610016, P.R. China