On-line haemodiafiltration versus low-flux haemodialysis. A prospective randomized study

Background. Current methods of renal replacement therapy lead only to an in significant removal of larger, potentially toxic, substances, which are exc reted by healthy kidneys. On-line preparation of substituate from dialysate and the use of high-flux membranes allow substantial convective removal of such substances. A modified on-line haemodiafiltration method with the use of a large membrane surface and a high convective part was chosen to test whether the elimination of larger substances, such as low-molecular-mass pr oteins, has a clinical impact. Methods. In a prospective, controlled study over 24 months, 44 unselected c hronic dialysis patients were randomized to undergo either low-flux haemodi alysis (HD; n = 21) or haemodiafiltration (HDF; n = 23). To eliminate confo unding factors, low-molecular efficacy was matched (Kt/V 1.8), and the same membrane material (polysulfone), ultrapure dialysate and the same treatmen t duration (4.5 h) were applied to each group. Results. Morbidity, mortality, blood pressure, dialysis-associated hypotens ive episodes, haematocrit and erythropoietin dose did not differ between th e groups. The same was true fbr body weight and, accordingly, bioimpedance values, clinical hydration score, skinfold thickness, plasma albumin, preal bumin and transferrin. beta(2)-Microglobulin in the plasma did not change i n the HD group and varied between 32 and 43 mg/l throughout the 2 years. In HDF, beta(2) microglobulin decreased from similar values to 18 mg/l predia lysis (P < 0.01) in the first 6 months of HDF treatment and then remained c onstant during the remaining 18 months. Conclusion. In the absence of any clinical marker of uraemic toxicity the r emoval of larger molecules over the time-span of 2 years during HDF had no clinical implication compared with extremely land for routine practice unre alistically) well-dialysed patients with low-flux HD. In the absence of any side-effects of on-line HDF and supposing that plasma beta(2)-microglobuli n is a marker of morbidity, on-line HDF ensures an excellent dialysis quali ty which apparently takes time to translate into measurable clinical sequel ae.