This study aims to compare high-efficiency post-dilution on-line hemodiafiltration and high-flux hemodialysis regarding mortality, hospitalization rate, several clinical and laboratory parameters, and required medications.

The investigators hypothesize that high-efficiency post-dilution on-line hemodiafiltration may provide better outcome, less morbidity, higher quality of life, and lesser requirement of medications.

The proposed controlled, randomized study aims to compare high-efficiency post-dilution on-line hemodiafiltration and high-flux hemodialysis regarding mortality, hospitalization rate, several clinical and laboratory parameters, and required medications.

Seven hundred and eighty HD patients will be taken into the study. The study will last for two years with an intermediate analysis at the first year. The patients will be randomly placed in two groups:

1. Post-dilution on-line hemodiafiltration,
2. High-flux hemodialysis.

In both groups, FX series high-flux helixone membranes will be used, duration of each session 240 minutes, and blood flow rates 250-400 ml/min. ONLINEplus integrated Fresenius 4008S machines will be used for on-line post-dilution HDF. Substitution volume will be above 15 liters in hemodiafiltration sessions.

Echocardiography for determination of left ventricular geometry, pulse wave velocity analysis to assess arterial stiffness, evaluation of nutritional and inflammatory state, assessment of life quality, depression and cost analysis will be performed.

Inclusion Criteria:

• older than 18 years
• on maintenance bicarbonate HD scheduled thrice weekly 12 hours/week,achieved mean single pool Kt/V above 1.2
• willingness to participate in the study with a written informed consent

Exclusion Criteria:

• To be scheduled for living donor renal transplantation
• To have serious life-limiting co-morbid situations, namely active malignancy, active infection, end-stage cardiac, pulmonary, or hepatic disease
• Pregnancy or lactating
• Current requirement for HD more than three times per week due to medical comorbidity
• GFR greater than 10 ml/min/1.73 m2 as measured by the average of urea and creatinine clearances obtained from a urine collection of at least 24 hours
• Use of temporary catheter
• Insufficient vascular access (blood flow rate lower than 250 ml/min)
• Mental incompetence