Inclusion Criteria:  signed informed consent Age older than 20 year old. End stage renal disease under regular hemodialysis with three times per week and duration of each session at least 4 hours Having at least consecutive 6 months data of both Hb and biochemical study during dialysis before enrollment and at least one Hb level within the range of 11-12 g/dl Having at least one prescription of ESA supplement to keep Hb within the range of 10-12 g/dl in the past 6 months before the enrollment Having received ESA of the same brand at least 6 months before the enrollment  Exclusion Criteria:  Ever receiving blood transfusion in the past 12 months Active bleeding with blood loss more than 250cc in 3 months before the enrollment Active infection or malignancy Study subject can not follow with the study protocol  End of Study  The eligible subject will not be allowed to continue the study once informed consent is withdrawn or event happening meets the following criteria: