On-line haemodiafiltration decreases serum TNFalpha levels in haemodialysis patients

Sir, Blood contact with the dialysis membrane has been documented as a major cause of cytokine activation and release. This interaction is associated with haemodialysis-related acute manifestations, such as fever and hypotension (less frequent at present) [1], and chronic morbidity like inflammation, malnutrition, atherosclerosis, cardiovascular disease, anaemia and even a higher mortality rate [1,2]. Increased cytokine productionuactivation may also be responsible for bone remodelling, participating in the stimulationuinhibition of osteoclasts and osteoblasts and the aggravation of b-2-microglobulin amyloidosis [3]. The response to erythropoietin in haemodialysis patients also seems to be mediated by various cytokines that participate directly in the erythropoietic process [4]. We had the opportunity to demonstrate that in a group of chronic haemodialysis patients the change from lowto high-flux polysulfone membranes permitted a significant reduction in erythropoietin requirements for the maintenance of a stable haemoglobin at 11.5 gudl [5]. These results may compensate, by saving erythropoietin, the increased cost associated with the use of high flux membranes and on-line haemodiafiltration. An increased cytokine activation secondary to blood exposition to bioincompatible dialysis components has been reported by several authors. Different cytokines are involved in the chronic inflammation that results from this bioincompatibility of the haemodialysis treatment.Among the cytokines most widely linked to the inflammatory response has emerged the tumour necrosis factor (TNFa). Unfortunately, most authors compare different types of membranes, with variable degrees of biocompatibility and diffusiveuconvective properties, making an individual evaluation of each of these properties very difficult as well as of their influence on cytokine activation. With the purpose of separately evaluating the effects of increased convective capacity on the serum levels of cytokines, we used synthetic membranes of the same type (polysulfone) during low-flux haemodialysis, high-flux haemodialysis and high-fluxqon-line haemodiafiltration. A prospective study was carried out in 24 patients who were on intermittent haemodialysis for )3 months. We measured the serum levels of C3c (185 kDa), C4 (205 kDa) and TNFa (19 kDa) at the beginning and end of the ‘mid-week dialysis session’ during three consecutive weeks. TNFa serum levels were measured by quantitative immunoassay RD systems. During the first week, a low-flux polysulfone was used (ultrafiltration coefficient between 11.1 and 18 mluhummHg); during the second week a high-flux polysulfone was used (ultrafiltration coefficient between 40 and 55 mluhummHg); and finally, during the third week the same membrane as the week before was used but with the on-line haemodiafiltration technique. All of these membranes were steam sterilized and not recycled. The blood pump rate was)300 mlumin and the dialysate pump rate was 800 mlumin. We used Nephrol Dial Transplant (2003) 18: 447