[Influence of the primary membrane on lipid apheresis selectivity in cascade filtration]

In apheresis, plasma separation from whole blood may be achieved by filtration. Some plasmapheresis membranes do not seem to be totally permeable to proteins: for instance, polyvinyl alcohol membrane presents apparent sieving coefficients significantly lower than 1, especially for apolipoproteins B (S' = 0.74 +/- 0.15). Moreover, severe membrane fouling is noticed during the treatment. The low permeability of the primary membrane for ApoB induces direct recirculation of this lipoprotein to the patient, without any chance of removal by the second membrane. In order to increase double filtration performance, it seems necessary to use plasmalfilters with a pore diameter of 0.5 microns. These filters are more permeable to plasma proteins and eliminate pathogenic protein better during the second stage of the process.