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Haemodialysis, by design, uses a semipermeable membrane to separate blood from dialysate. The qualities of this membrane determine the nature of the ‘traffic’ between the blood and dialysate. In this sense, the qualities of the membrane determine what size molecules move from one compartment to the other, the amount and rate at which they might move and the amount and rate of water movement across the membrane. In addition, the nature of the membrane influences the biological response of the patient both in terms of what is or is not removed by the dialysis process and by way of the reaction to the biocompatibility of the membrane. This brief review will explore aspects of dialysis membrane characteristics. [ABSTRACT FROM AUTHOR]

Aim: Vitamin deficiencies are common in patients with end-stage renal disease (ESRD) owing to dietary restrictions, drug–nutrient interactions, changes in metabolism, and vitamin losses during dialysis. The present study investigated the levels of serum and red blood cell (RBC) folate, plasma pyridoxal-5′-phosphate (PLP), serum cobalamin, blood thiamine, blood riboflavin, and plasma homocysteine (tHcy) before and after haemodialysis treatment. Methods: Vitamin and tHcy blood concentrations were measured in 30 patients with ESRD before and after dialysis session either with low-flux ( n = 15) or high-flux ( n = 15) dialysers. Results: After the dialysis procedure, significantly lower concentrations of serum folate (37%), plasma PLP (35%), blood thiamine (6%) and blood riboflavin (7%) were observed. No significant changes were found for serum cobalamin or for RBC folate. There were no differences in the washout of water-soluble vitamins between treatments with low-flux and high-flux membranes. Furthermore, a 41% lower concentration in tHcy was observed. The percentage decrease in tHcy was significantly greater in the patients treated with high-flux dialysers (48% vs 37%; P < 0.01). The percentage change during dialysis was significantly inversely related to the molecular weight of the vitamins measured ( r =−0.867, P < 0.01). Conclusion: This study showed significantly lower blood or serum levels of various water-soluble vitamins after dialysis, independently of the dialyser membrane. The monitoring of the vitamin status is essential in patients treated with high-flux dialysers as well as in patients treated with low-flux dialysers. [ABSTRACT FROM AUTHOR]