Recent trials on hemodiafiltration.

The theoretical advantages of high-flux hemodialysis (HD) in treating patients with chronic kidney disease (CKD) stage 5 are related to the higher toxin removal (especially 'middle molecules'), including sodium and water, and to the better biocompatibility of the treatment, including membrane and water quality. Several observational studies have shown that high-flux HD has positive effects on the survival and morbidity of uremic patients when compared with low-flux HD. The primary analysis of the prospective randomized HEMO (Hemodialysis Outcomes) study showed that high-flux HD was associated with an 8% nonsignificant reduction of mortality in comparison with low-flux HD. However, a secondary analysis pointed to an advantage for high-flux HD in subgroups of patients. More recently, the MPO (Membrane Permeability Outcome) study found that survival could be significantly improved by using high-flux HD compared with low-flux HD in high-risk patients as identified by serum albumin ≤4 g/dl and, in a post hoc analysis, in diabetic patients as a whole. On-line hemodiafiltration (HDF) is considered the most efficient technique of using high-flux membranes. Clearance of small solutes like urea are higher than in hemofiltration, and clearance of middle solutes like β(2)-microglobulin are higher than in high-flux HD. Since there is only a very limited number of randomized prospective trials comparing HDF and high-flux HD, no conclusive data are available about the effect of increased convection of on-line HDF on survival and morbidity of CKD patients. The suggested advantages of HDF must be confirmed by a large randomized controlled study.