Study of three patients with thrombotic thrombocytopenic purpura exchanged with solvent/detergent-treated plasma: is its decreased protein S activity clinically related to their development of deep venous thromboses?

Solvent/detergent treated plasma (S/DP) has reduced protein S activity (about 0.5 units/mL) as compared with fresh frozen plasma (FFP). When used as replacement fluid for repetitive therapeutic plasma exchange (PEX), e.g., in patients with thrombotic thrombocytopenic purpura (TTP), S/DP could lead to lowered protein S levels and, possibly, risk of hypercoagulable complications. We describe three patients with TTP who had low functional protein S (FPS) levels during PEX for TTP. Each developed one or more deep vein thromboses (DVTs) while receiving 100% S/DP or 50% S/DP and 50% cryosupernatant plasma (CSP) as replacement fluid. FPS levels rose when 100% CSP was substituted for S/DP. Our observations suggest that use of S/DP alone or in 50% combination with CSP as replacement fluid in PEX for TTP may lead to difficulty in maintaining safe FPS levels. Determination of risk of resulting clinically significant thrombotic events requires further study. Copyright 2000 Wiley-Liss, Inc.