Can sterile and pyrogen-free on-line substitution fluid be routinely delivered? A multicentric study on the microbiological safety of on-line haemodiafiltration

Background. Microbial contamination is characterized not only by the presen ce of bacteria, but also by high concentrations of biologically active by-p roducts. They are potentially able to cross ultrafiltration and dialysis me mbranes and stimulate immunocompetent blood cells to synthesize cytokines. In turn, cytokine induction causes acute symptoms and has been incriminated in the long-term complications of haemodialysis patients. Infusion of larg e volumes of substitution fluids following ultrafiltration of microbially c ontaminated dialysis fluids may place patients on on-line therapies at part icular risk. Methods. In this study we evaluated 30 machines with a two-stage ultrafiltr ation system in routine clinical haemodiafiltration settings in six centres for 6 months. Microbiological safety was assessed monthly and at the last use of the filters by determining microbial counts, endotoxin concentration and cytokine-inducing activity. Results. No pyrogenic episodes were observed during the study period. Doubl e-filtration of standard dialysis fluid (range, <1-895 cfu/ml, 0.0028-4.682 2 IU/ml) resulted in sterile substitution fluids with endotoxin concentrati ons well below the Ph.Eur. standard for haemofiltration solutions (range, 0 .0014-0.0281 vs 0.25 IU/ml). Moreover, they did not differ from commercial haemofiltration solutions and depyrogenated saline. Likewise, there was no difference in the cytokine inducing activity between the solutions tested. The high microbiological quality of the ultrafiltered dialysis fluid, which was in the same range as substitution fluid, translates into both the abse nce of cytokine induction by dialyser back-transport and a redundant safety mode of the on-line system by a second filtration step. Conclusion. On-line HDF treatment can routinely be provided with ultra-pure dialysis fluids and sterile substitution fluids at pyrogen-free levels. Th e on-line preparation of substitution fluids thus can be considered microbi ologically safe.