Comparison of Clinical Performance and Hemocompatibility of Dialyzers Applied During Post-dilution Online Hemodiafiltration

Inclusion Criteria: General: * Minimum age of 18 years * Existing informed consent form signed and dated by study patient as well as investigator/authorized physician * The patient is legally competent and able to understand the nature, risks, meaning, and consequences of the clinical trial and can subsequently declare her/his consent for participation in the clinical trial (cf. European Medical Device Directive and corresponding national regulations) * Patients with a chronic kidney disease stage 5D (end stage renal disease with a glomerular filtration rate of 15 ml/min or less) on hemodiafiltration as extracorporeal renal replacement therapy Study-specific: * On online post-dilution hemodiafiltration (HDF), at least 4 h treatment time thrice weekly with FX or FX CorDiax dialyzer ≥ 1 month * Vascular access (fistula or graft) which enables blood flow rate ≥ 300 ml/min Exclusion Criteria: General: * Any condition which could interfere with the patient's ability to comply with the study. This decision is at the discretion of the treating physician and relates to the general stable condition of the patient (e.g. any acute condition, e.g. infection or mental problem which might give reason for concern etc.) * Ongoing participation in an interventional clinical study during the preceding 30 days * Previous participation in this study * Pregnancy (pregnancy test will be conducted at start and end of study with female patients aged \< 55 years) or lactation period * Patient is not able to give informed consent according to the European Medical Device Directive and corresponding national regulations Study-specific: * Recurrent episodes of vascular access failure characterized by e.g. repeated cannulation problems or unstable blood flows within the last 2 months prior to study start (\>3 times, respectively) * Repeated single needle treatments (\>3 times within the last 2 months prior to study start) * Catheter as vascular access * Unstable patients (due to e.g. acute intercurrent disease like cardiovascular infarction, decompensated heart failure, cerebrovascular accident, severe infection, active malignant disease) * Patients with NYHA ≥ 3, COPD (GOLD 2-4), frequent intradialytic symptomatic hypotension * Patients with known or suspected allergy to trial product and related products * Patients with known inborn or acquired deficiencies of the innate and/or adaptive immune system * Patients with acute (use within last 4 weeks) and/or chronic immunosuppressive medication e.g. due to immune-mediated disease including autoimmune diseases, transplantation, or cancer (oral and systemic corticosteroids, calcineurin and mTOR-inhibitors, immunosuppressive monoclonal antibodies, cytotoxic chemotherapy) * Planned absence from dialysis unit within the 14 weeks of study duration e.g. due to scheduled hospitalization, holidays or any other reason * Active HBV, HCV, HIV, SARS-CoV-2 infection, as well as any other febrile illness * Reported SARS-CoV-2 infection with or without symptoms within the 12 weeks before inclusion into the study * Unwillingness to undergo repeated SARS-CoV-2 infection testing