HDF promise for the future.

Sir, The February issue of Nephrology Dialysis Transplantation amply reported on online haemodiafiltration (HDF) as a possible promise for the future [1]. Please note the following erratum in Table 1 of the Editorial Comment, concerning our study with reference 16: high-volume HDF in postdilution was compared with high-flux haemodialysis (hfHD) with regard to the removal of beta2-microglobulin (b2M) and not with low-flux HD (lfHD), as is reported. Although most studies with online HDF demonstrate a higher removal of a broad range of the molecular spectrum of uraemic compounds versus HD, confusion still persists on the preferred method of HDF. With regard to the location of inflow of the substitution fluid, most studies rely on post-, pre-, mid- or mixed dilution, but this results in different removal rates. It is regrettable that in several references in the Editorial Comment, even the used HDF method was not mentioned (Table 1). Yet this is essential for the knowledge of the efficiency of the treatment. For instance, it is well known that with high-volume predilution HDF, a lower clearance of small molecules is achieved versus high-flux HD. Besides, a lower b2M clearance is noted in high-volume predilution HDF, compared with postdilution HDF with the same amount of substitution volume (80 ml/min) [2]. In view of these results, it is not surprising that in the ongoing trials in the Netherlands and France high-volume HDF in postdilution is chosen. It is also stated in the Editorial Comment that conflicting results concerning phosphate clearance were reported. When comparing phosphate removal with high-volume (100 ml/min) HDF in postdilution, our group observed a 19% higher removal versus high-flux HD [3]. Finally—as in our department, routine high-volume postdilution HDF is performed since 1993—in dialysis patients with more than 10 years of treatment, a lower prevalence of carpal tunnel syndrome is reported in reference 16 of the Editorial Comment. Concerning survival, recently our group reported a 26% survival benefit [4], comparable with the data of the DOPPS study and of the observational study from Eastern Europe. Conflict of interest statement. None declared.