Membrane plasmapheresis in the United States: a review over the last 20 years.

Plasmapheresis is a general term involving extracorporeal plasma separation by centrifugation or primary membrane plasma separator (MPS). Further plasma processing can be accomplished by the use of secondary membrane plasma fractionation (PF), as in double filtration plasmapheresis, also called cascade filtration, low-density lipoprotein pheresis, thermofiltration, and cryofiltration apheresis. Otherwise, the separated plasma is replaced by colloid solution as in plasma exchange (PE). PE is used, unselectively, to treat patients with immunological, neurological, hematological, renal, and metabolic disorders. Secondary PF may be a more selective alternative. In general, the primary MPS and secondary PF are safe, effective, and biocompatible. The advantages of the primary MPS include its simplicity to use with blood pumps and no observed white blood cell or platelet loss, compared with centrifugation. The disadvantages are lack of versatility, the need to monitor transmembrane pressure to prevent hemolysis, and possible biocompatibility issues such as use of polyvinyl alcohol membranes. The advantages of secondary PF, compared with PE, include selective removal of macromolecules according to molecular weight and filter pore size. No deficiency syndromes or sepsis are observed, nor is replacement solution required. More than 1 plasma volume may be processed, and it is less expensive than PE. Cryofiltration apheresis, using the cryoglobulin filter, selectively removes cryoproteins and is a specific treatment for cryoprecipitate-induced diseases. The disadvantages of PF include biocompatibility, especially with concomitant ACE inhibitor use, and membrane plugging. An important disadvantage is that most PFs are investigational in the United States. This article reviews the availability, safety, efficacy, and biocompatibility of primary MPSs and secondary PF in the United States.