In China, the estimated prevalence of patients with ESRD receiving PD or maintenance HD increased from 51.7 per million population (pmp) at the end of 2007 to 79.1 pmp at the end of 2008. Theranova 400 is designed to deliver the performance of hemodiafiltration (HDF) using standard hemodialysis (HD) equipment and treatment mode, including HD machines, disposables, blood and dialysate flows, length of treatment and frequency of treatment. Theranova 400 utilizes a Medium Cut-Off (MCO) membrane with extended permeability for middle solutes to closely modulate the removal function of the kidney without the complexity of HDF. The primary objective of the study is to demonstrate non-inferiority of the Theranova Dialyzer in hemodialysis (HD) mode compared to hemodiafiltration (HDF), using FX 800 in HDF mode. Comparison of the study arms over time will be used to support the safety of Theranova 400 by demonstrating stable serum albumin levels, as well as support the dialyzer's efficacy to significantly remove serum middle molecules.

Inclusion Criteria:

• Patients aged 18 years or older.
• Patients who are able to give IC after an explanation of the proposed study.
• Patients who have Kt/Vurea > 1.2 for the last 2 measurements, with the most recent Kt/Vurea measurement taken within 4 weeks before or during study screening.
• Patients with a dialysis prescription (dialyzer, time, dialysis fluid flow rate (QD), blood flow rate (QB)) stable over 6 recent treatments. The dialysis treatment time should be 3.5 to 4.5 hours per session with minimum QB of at least 250 mL/min and QD of 500 mL/min.
• Patients who are on stable anticoagulation prescription and dose.
• Patients with ESRD receiving chronic HD treatment with a history of thrice weekly HD, and at least 1 HDF session within 1 month prior to study.
• Patients who have been stable on in-center HD for >3 months prior to study enrollment
• Patients who have an adequate arteriovenous (AV) fistula or graft, or dual-lumen tunneled catheter capable of providing a blood flow rate of at least 250 mL/min.
• Patients with a minimum total convective volume (including ultrafiltration (UF)) of 16 L post-dilution for the most recent HDF treatment.
• Patients who receive in-center treatment hemodialysis at a site that routinely implements high flux dialysis and HDF.

Exclusion Criteria:

• Patients who have acute renal failure with the chance for recovery.
• Patients who are pre-scheduled for a living donor kidney transplant within the next six months, who plan a change to PD within the next six months, or who require single-needle dialysis therapy.
• Pregnant and lactating women.
• Patients with positive serology tests for Hepatitis B surface antigen, Hepatitis C total antibody), HIV and Syphilis.
• Patients with known hemodynamic instability, anemia (Hgb < 90 g/L), and/or patients with Hgb >130g/L for coagulation risk.
• Patients who are severely malnourished or with significant disease that interferes with liver synthetic function, e.g. with serum albumin <35 g/L.
• Patients with active or ongoing infection as per investigator's judgement.
• Patients with history of solid tumors requiring anti-cancer therapy in the past or next 6 months, or life expectancy less than 1 year, or patients or with history of hematology neoplasm.
• Patients diagnosed with a NYHA Class IV congestive heart failure, or acute coronary syndrome and/or who have suffered a myocardial infarction within three months prior to the start of the study.
• Patients with a history of severe mental disorders.
• Patients who are currently participating in, or have previously participated in other interventional clinical trials during the past 4 weeks.
• Patients who have had an allergic response to polyarylethersulfone (PAES) or polysulfone (PS) membrane or have history of poor tolerance to dialyzers with synthetic membranes
• Patients with advanced liver, heart or pulmonary disease as judged by the Investigator.
• Patients with any comorbidity possibly conflicting with the study purpose or procedures as judged by the Investigator.