This is a prospective cross-over study including 10 stable hemodialysis patients with chronic kidney disease stage 5. The cross-over study lasts 2 weeks with the study dialysis sessions at midweek.

During one session, the patient will be dialyzed during 4 hours with high volume post dilution hemodiafiltration (HDF) with an FX800 hemodialyzer (Fresenius Medical Care) and a blood flow of 300mL/min, dialysate flow of 500mL/min, and substitution flow of 75mL/min.

During the other midweek session, the patient will be dialyzed during 8 hours with high flux hemodialysis (HD) with an FX80 hemodialyzer (Fresenius Medical Care) and a blood flow of 200mL/min and a dialysate flow of 500mL/min.

The HDF and HD sessions will be randomized. Blood samples will be drawn pre and post dialysis from the arterial blood line, and after 30min after dialysis start, a blood sample will be drawn from the inlet and outlet line.

At the dialysate outlet line, partial dialysate collection is performed at the outlet line.

Blood and dialysate samples will be analyzed for a broad range of retention solutes like small and water soluble solutes, middle molecules, and protein bound solutes.

These data will be further used to calculate solute removal and evaluate any differences between the solute removal during high volume post dilution HDF and high flux HD.

Inclusion Criteria:

• Chronic kidney disease (CKD) stage 5 with hemodialysis or hemodiafiltration treatment for more than three months.
• No vascular access related problems (Arteriovenous (A/V) fistula, graft or bi-flow catheter)
• Double needle/lumen vascular access
• No ongoing infection
• Singed informed consent form

Exclusion Criteria:

• Inclusion criteria not met
• Known HIV or active hepatitis B or C infection (Positive Polymerisation Chain Reaction (PCR))
• Pregnancy
• Unstable clinical condition (e.g. cardiac or vascular instability)
• Known coagulation problems
• Patients participating in another study interfering with the planned study.