This randomized, crossover study aims to investigate the intradialytic kinetics of selected cardiac biomarkers in patients with end-stage renal disease treated with dialysis. The cardiac biomarkers of interest include high-sensitivity cardiac troponin I, high-sensitivity cardiac troponin T, brain natriuretic peptide, and a novel cardiac biomarker named secretoneurin.

In 24 patients treated with maintenance hemodialysis, the study will compare high-flux hemodialysis (HD) with post-dilution hemodiafiltration (HDF) to investigate:

• Baseline concentrations and week-to-week plasma variations of the cardiac biomarkers.
• Changes in the plasma concentrations of the cardiac biomarkers during high-flux HD and post-dilution HDF.
• Dialyzer clearance of the cardiac biomarkers in high-flux HD and post-dilution HDF.
• Adherence of the cardiac biomarkers to the dialyzer membrane.
• Concentrations of the cardiac biomarkers 30 minutes post-dialysis to investigate a potential rebound effect.

Additionally, a sub-study of 24 patients treated with peritoneal dialysis will investigate the baseline concentrations and week-to-week plasma variations of the same cardiac biomarkers.

Patients treated with maintenance hemodialysis:

Single-center, randomized, crossover study with 24 participants. The study will investigate the effect of high-flux HD (using the FX CorDiax 100 dialyzer) and post-dilution HDF (using the FX CorDiax 1000 dialyzer) on the intradialytic kinetics of selected cardiac biomarkers. The study will not be blinded, but the order of the interventions will be randomized. The two dialysis sessions will be conducted on the same weekday. Between the two interventions, the patient will have a wash-out period of 1-3 weeks with standard dialysis treatment.

On both trial days, the following dialysis settings will be the same for each individual patient:

• The dialysis sessions will last 4 hours.
• The same dialysis machine will be used, either the Fresenius Medical Care 5008 or 6008 CAREsystem machine.
• Same vascular access will be used.
• The composition of electrolytes in the dialysate will be the same.
• Blood flow rate will be >300 mL per minute and consistent.
• Dialysate flow rate will be 500 mL per minute.
• Ultrafiltration rate will be constant aiming at dry weight.
• Routine anticoagulation protocol will be unchanged, but consistent on both trial days.
• Routine dialysate temperature will be unchanged, but consistent on both trial days.

On both trial days, different baseline characteristics will be gathered, including demographic data, clinical data, dialysis characteristics, and routine blood samples. Blood samples, for the analysis of the selected cardiac biomarkers, will be collected:

• Before the dialysis session is started (baseline).
• After 10, 30, 60, 120, 180, and 240 minutes of dialysis. All samples will be collected from the blood dialyzer inlet; however, halfway into the dialysis session (after 120 minutes), samples will also be collected from the blood dialyzer outlet and from the dialysate.
• 30 minutes after dialysis cessation. However, if the patient will not stay 30 minutes, the post-dialysis sample will be gathered after 5 minutes.

Sub-study of patients treated with peritoneal dialysis:

In a sub-study, 24 patients treated with peritoneal dialysis, will be included for one or two venous blood samples (with a minimum of 1 week between) to determine the baseline concentration and week-to-week variation of the cardiac biomarkers of interest. On both trial days, different baseline characteristics will be gathered, including demographic data, clinical data, dialysis characteristics, and routine blood samples.

Inclusion Criteria:

• Age of 18 years or older.
• Clinically stable patients with end-stage renal disease treated with maintenance hemodialysis or peritoneal dialysis.
• Regarding patients treated with hemodialysis: Dialysis access with an arteriovenous fistula and able to maintain a blood flow rate >300 mL.

Exclusion Criteria:

- Not able to understand or sign informed consent.