Phosphate clearance for bleach reprocessed polysulfone hemodialyzers: effects of electrostatic interactions

Hyperphosphatemia is a major problem for hemodialysis patients due to inadequate phosphate clearance during dialysis. The objective of this study was to understand the effects of bleach reprocessing on phosphate clearance. Data were obtained using Fresenius polysulfone dialyzers exposed to bleach in an in vitro dialysis. The phosphate clearance decreased slightly after a single reprocessing cycle, with more than a 10% reduction observed after 15 cycles. Streaming potential measurements showed that bleach reprocessing caused an increase in the negative charge on the polysulfone membrane, suggesting that the change in phosphate clearance was due to an increase in electrostatic repulsion. The changes in clearance and surface charge were consistent with theoretical calculations of the effects of electrostatic interactions on solute diffusion. These results provide the first evidence that bleach reprocessing can reduce phosphate clearance due to electrostatic interactions between the phosphate anion and negatively charged dialysis membranes.