Quantitative Mass Transfer of SFP-iron From Dialysate to Blood in CKD-HD Patients

* A total of 12 subjects on standard 3X/week hemodialysis will be studied in 2 groups (6 subjects per group) * 2 primary dialyzer membranes will be studied.: * Polyamide Membrane (Gambro Polyflux series: 17R and 21R) * Cellulose Triacetate (Baxter CT series: CT-190) * Each 1-week treatment cycle will include 3 haemodialysis (HD) sessions per subject, including 2 study treatment-HD sessions and 1 non-treatment-HD session per subject. Treatment-HD sessions will be conducted midweek and end-of-week (i.e. Dialysis days 3 and 5 of each week with a 1 day interdialytic interval) to avoid excessive fluid shifts due to the increased UF needed during the non-treatment HD session (conducted at beginning of the week; HD day 1). * Within each group, each subject will be randomized to 1 of 6 treatment sequences. The treatments to be investigated are: Control; new dialyzer, reused dialyzer, low blood flow/dialysate flow, Low bicarbonate concentration and a different synthetic dialyzer membrane (PAES) * Blood for a complete serum iron profile over time will be obtained during the new dialyzer (SFP/standard bicarbonate/new dialyzer/ high Qb and Qd) for all subjects. This will necessitate approximately a 24-hour inpatient confinement to obtain blood at specified time intervals after dialysis is completed. Blood for a partial iron profile will be collected during the dialysis sessions at all other dialysis sessions. * Each of the 6 enrolled subjects per dialyzer membrane type will be assigned to a different sequence of treatments to help ensure that the treatment sequence does not affect the analysis (Note: the first dialysis sessions of each of the 3 study weeks, i.e. HD1, HD4 and HD7, are non-study related sessions during which no study procedures are performed except for adverse event collection. * Patients should not be receiving any of the following medications from screening through the end of the study: * Oral iron preparations, including multivitamin supplements containing iron * Intravenous iron preparations * Doses of ESA's should not be changed from screening to the end of the study.