DETERMINATION OF CONTACT PHASE ACTIVATION BY THE MEASUREMENT OF THE ACTIVITY OF SUPERNATANT AND MEMBRANE SURFACE-ADSORBED FACTOR-XII (FXII)- ITS RELEVANCE AS A USEFUL PARAMETER FOR THE IN-VITRO ASSESSMENT OF HEMODIALYSIS MEMBRANES

We investigated hemodialysis membrane biocompatibility with respect to contact phase activation by determination of FXII-like activity (FXII A) on the membrane surface and in the supernatant phase, during plasma contact with various hemodialysis membranes using an in vitro incubat ion test cell. The results were compared to the influence of these mem branes on the activation of purified FXII. A time course for the gener ation of activated FXII using purified FXII solution at physiologic co ncentrations on two similar negatively charged polymers was performed. The membranes assessed were regenerated cellulose (Cuprophan; Akzo Fa ser AG, Germany), modified cellulosic (Hemophan; Akzo Faser AG), acryl onitrile-sodium methallyl copolymer-based membrane AN69S (Hospal, Fran ce), and SPAN, a new polyacrylonitrile-based copolymer (Akzo Nobel AG) . The plasma FXIIA at the membranes surface was significantly differen t between the membranes, while the supernatant phase FXIIA exhibited n o significant differences. In contrast, activation of purified FXII in a plasma-free system with respect to supernatant activity indicated s ignificant differences between the materials. A similar finding for th e membrane-bound factor XIIA was also observed when purified factor XI I was used. The membrane-bound FXIIA values observed in the plasma sys tem containing heparin were significantly greater than in citrated pla sma. This demonstrated the strong influence of heparin and the interac tion of other plasma components to the membrane surface on the activat ion of contact phase of coagulation. (C) 1996 John Wiley & Sons, Inc.