Current topics on cryofiltration technologies.

In the last 40 years, therapeutic plasmapheresis techniques have been improving considerably. These include cryofiltration technologies providing novel ways of removing large amounts of cryoproteins from plasma. The concept of cryofiltration involves exposure of plasma to below core (37 degrees C) and room temperatures (25 degrees C) without freezing. It was initially used to treat diseases such as cryoglobulinemia with systemic vasculitis, rheumatoid arthritis, systemic lupus erythematosus, and ABO-incompatible transplants. There are 2 basic types of cryofiltration. The first method removes cryoproteins, namely cryoglobulins that precipitate at 4 degrees C. Several filters have been used for this procedure like the AP06M (Asahi Medical, Tokyo, Japan) with a 0.2 microm pore size, a 0.65 m2 surface area, and a cellulose diacetate (CDA) membrane. It has been used in the United States and Japan for treatment of rheumatoid arthritis and cryoglobulinemia. A major disadvantage was frequent filter plugging, which was cumbersome and it is no longer used in the United States. The G3 cryofilter (Gelman Sciences, Ann Arbor, MI, U.S.A.) with a 3 microm pore size was tried in vitro but proved inadequate by design. Currently in our institution, the cryoglobulin filter (Pall Medical, Ann Arbor, MI, U.S.A.) is used with a 4.3 microm pore size, a 0.135 m2 surface area, and an acrylic co-polymer pleat membrane. We performed over 1,200 procedures in 40 patients in the last 8 years. The second type of cryofiltration removes cryogel, which is an agglutination complex of fibrinogen, fibronectin, fibrin split products, and cold insoluble proteins with a heparin core, at temperatures between 2 and 10 degrees C. The AP06M, the AC1740 (Asahi Medical) with a 0.02 microm pore size, a 1.70 m2 surface area, and a CDA membrane, and the Evaflux-4A (Kuraray Company, Osaka, Japan) with a 0.03 microm pore size, a 2 m2 surface area, and an ethylene vinyl alcohol membrane are used to remove cryogel to treat ABO-incompatible transplants as well as rheumatoid arthritis and other previously mentioned diseases. This article will discuss each cryofiltration treatment modality.