In patients on maintenance hemodialysis (HD), protein energy wasting (PEW) defined as loss of muscle mass and fuel reserves of the body is frequent and associated with severe morbidity and mortality. Several factors, including inflammation, oxidative stress, metabolic disorders, loss of nutrients, diabetes, retention of middle molecule uremic toxins and dialysis procedure contribute to PEW. It has been previously reported that intensive HD treatments such as short daily and nocturnal HD may improve nutritional parameters. Moreover, post-dilution Online hemodiafiltration (OL-HDF) may also improve PEW by preserving lean body mass evaluated by bioimpedance analysis (BIA) probably through decreased inflammation, stimulation of appetite and better removal of uremic toxins. The recently developed medium cut-off dialyzer (MCO) in HD has demonstrated efficient depuration of middle uremic toxins as compared to high flux HD (HF-HD), similar to that of OL-HDF. Both MCO-HD and OL-HDF may exert beneficial effects on PEW, since they increase removal of higher weight middle molecules, which mostly encompass proteins related to inflammation and PEW in the uremic milieu

In a previous randomized study, we found, that after 3 months, MCO-HD was associated with higher middle molecules removal and significant decrease in beta2-microglobulin, oxidized low-density lipoprotein, kappa and lambda free light chain pre-dialysis levels, without change in other inflammatory and oxidative stress biomarkers. In addition, compared to HF-HD, a modulation of inflammation has been demonstrated with MCO-HD in another randomized trial. After 3 months, MCO-HD was shown to downregulate the expression of the pro-inflammatory IL-6 and tumor necrosis factor (TNF) mRNA in peripheral leucocytes. Moreover, higher removal and decrease in TNF alpha level with concurrent reduced resistance to erythropoiesis stimulating agents (ESA) has been also reported with MCO-HD. However, the long-term effects of MCO-HD on inflammatory, uremic toxins and malnutrition biomarkers remain to be established.

To test the hypothesis that MCO-HD may positively affect body composition and nutritional status in HD patients we performed a 12-month single center retrospective pilot study. Compared to HF-HD, MCO-HD resulted in an improved variation rate of serum pre-dialysis creatinine level, lean tissue, skeletal muscle mass and index assessed by BIA, which are presumably good surrogate markers of PEW.

The aim of the present prospective, controlled randomized study is to evaluate the effect of MCO-HD on PEW, compared to standard HF-HD in chronic hemodialysis patients.

Inclusion Criteria:

• Patients able to give signed informed consent
• Age ≥ 18 years
• Patients established on HF-HD trice weekly four hour-sessions for at least 3 months.
• Patients able to walk
• Body mass index ≥ 20 and < 40 Kg/m2

Exclusion Criteria:

• Any uncontrolled medical condition, psychiatric disorder or biological abnormality that might interfere with subject's participation or ability to sign an informed consent.
• Implanted pace maker or cardioverter defibrillator
• Pregnant or breast-feeding women
• Active malignant disease, chronic inflammatory disease or other critical illnesses that may interfere with inflammatory parameters. Baseline C-reactive protein > 35 mg/l.
• Amputated limbs
• Prescription of oral or intra venous nutrition supplements
• Significant residual kidney function as defined by an urine output > 500 mL