Background. Compared to high-flux dialysis membranes, novel medium cut-off (MCO) membranes show greater permeability for larger middle molecules. Methods. In two prospective, open-label, controlled, randomized, crossover pilot studies, 39 prevalent hemodialysis (HD) patients were studied in four dialysis treatments as follows: study 1, three MCO prototype dialyzers (AA, BB and CC with increasing permeability) and one high-flux dialyzer in HD; and study 2, two MCO prototype dialyzers (AA and BB) in HD and high-flux dialyzers in HD and hemodiafiltration (HDF). Primary outcome was lambda free light chain (λFLC) overall clearance. Secondary outcomes included overall clearances and pre-to-post-reduction ratios of middle and small molecules, and safety of MCO HD treatments. Results. MCO HD provided greater λFLC overall clearance [least square mean (standard error)] as follows: study 1: MCO AA 8.5 (0.54), MCO BB 11.3 (0.51), MCO CC 15.0 (0.53) versus high-flux HD 3.6 (0.51) mL/min; study 2: MCO AA 10.0 (0.58), MCO BB 12.5 (0.57) versus high-flux HD 4.4 (0.57) and HDF 6.2 (0.58) mL/min. Differences between MCO and high-flux dialyzers were consistently significant in mixed model analysis (each P < 0.001). Reduction ratios of λFLC were greater for MCO. Clearances of α1-microglobulin, complement factor D, kappa FLC (κFLC) and myoglobin were generally greater with MCO than with high-flux HD and similar to or greater than clearances with HDF. Albumin loss was moderate with MCO, but greater than with high-flux HD and HDF. Conclusions. MCO HD removes a wide range of middle molecules more effectively than high-flux HD and even exceeds the performance of high-volume HDF for large solutes, particularly λFLC.

The general objective assigned to the EUropean DIALlysis (EUDIAL) Working Group by the European Renal Association-European Dialysis and Transplant Association (ERA-EDTA) was to enhance the quality of dialysis therapies in Europe in the broadest possible sense. Given the increasing interest in convective therapies, the Working Group has started by focusing on haemodiafiltration (HDF) therapies. Several reports suggest that those therapies potentially improve the outcomes for end-stage renal disease patients. Europe is the leader in the field, having introduced the concept of ultra-purity for water and dialysis fluids and with notified bodies of the European Community having certified water treatment systems and online HDF machines. The prevalence of online HDF-treated patients is steadily increasing in Europe, averaging 15%. A EUDIAL consensus conference was held in Paris on 13 October 2011 to revisit terminology, safety and efficacy of online HDF. This is the first report of the expert group arising from that conference.

The elimination of protein-bound compounds into dialysate is predicted by the level of pre-treatment plasma concentrations and depends particularly on diffusion. Lacking enhanced removal in online post-dilution haemodiafiltration emphasizes the minor significance of convection for the clearance of these solutes. Compared to LMW proteins, the highly protein-bound toxins pCS and IS are less effectively eliminated with all treatment forms. For a sustained decrease of pCS and IS plasma levels, alternative strategies promise to be more efficient therapy forms.

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On-line mid-dilution HDF with the Nephros OLpur MD 190 hemodiafilter appears to be a true technologic step ahead in terms of improved middle molecule removal. This efficient procedure gives hope to play a role in preventing or at least retarding dialysis-related long-term complications, such as beta(2)m amyloidosis, in ESRD patients, and may contribute to a more adequate dialysis therapy.

The estrogenic endocrine-disrupting substance bisphenol A (BPA) is extensively used as a starting material for a variety of consumer plastic products including dialyzer materials. The present study was performed to explore plasma BPA levels in patients with impaired renal function and to investigate if dialyzers differing in elutable BPA influence plasma levels in patients on maintenance hemodialysis. In vitro BPA was eluted from high-flux polyethersulfone (PUREMA H, referred as PUR-H), high-flux polysulfone (referred as HF-PSu), and low-flux polysulfone (referred as LF-PSu) dialyzers by recirculation with water for 180 min. In a cross-sectional clinical study, plasma BPA levels of outpatients with different stages of chronic kidney disease (CKD) from four different centers were determined. Furthermore, in a prospective, randomized, and crossover setting, 18 maintenance dialysis patients were subjected successively to 4 weeks of thrice-weekly hemodialysis with each LF-PSu, HF-PSu, and PUR-H. In addition, the fractions of protein-bound and free BPA were determined in a subset of dialysis patients. The mass of BPA eluted from the blood compartments in vitro under aqueous conditions varied for the three dialyzers being very low for PUR-H (6.2 ± 2.5 ng; P < 0.001), intermediate for HF-PSu (48.1 ± 7.7 ng), and highest for LF-PSu (140.8 ± 38.7 ng; P < 0.01). In 152 prevalent patients with CKD enrolled in the cross-sectional trial, plasma BPA started to rise after stage 3. Maintenance hemodialysis patients had more than six times higher BPA concentrations than patients with CKD stage 5 not yet on dialysis (10.0 ± 6.6 vs. 1.6 ± 1.8 ng/mL; P < 0.001). The BPA concentrations highly and inversely correlated with renal function. In the randomized controlled study, the plasma BPA concentrations were highly elevated compared with healthy controls (range 9.1 ± 4.5-12.0 ± 6.0 ng/mL vs. ≤0.2 ± 0.1 ng/mL; P < 0.001), but no change of the plasma levels was observed during hemodialysis with any of the three dialyzers in the course of a single treatment and over a period of 4 weeks. The protein-bound fraction of plasma BPA in the dialysis patients was 74 ± 5%. Renal function and, most likely, the total quantity of ingested BPA are essential parameters affecting plasma BPA concentrations. Dialyzers are one additional source of BPA, but differences in the elutable BPA content are not associated with a significant effect on BPA plasma levels in Western European maintenance dialysis patients. Due to high protein binding, the removal of BPA by hemodialysis is limited.

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