The independent Ethics Committee at Sichuan University affirmed that neither an ethics committee approval nor patient consent was necessary for this retrospective study. We conducted a retrospective case series study of all adult patients (age > 18 years) who were admitted to West China Hospital (the second most popular class 3A hospital located in Chengdu Sichuan province of China) with a confirmed diagnosis of AP, between December 2015 and June 2016.