Decrease and rapid recovery of protein C after plasma exchange

The anticoagulant protein, protein C (PC), was measured after 40 plasma exchanges (PEs) in 26 patients treated for a variety of disorders, most of which were immunological in nature. After 27 PEs involving exchange of 50 percent of the plasma volume with albumin and saline, mean PC activity and antigen decreased in parallel to about one-half normal levels, with good correlation between the two assays. Antithrombin III and prothrombin decreased to about the same levels as PC, with no significant differences between the percentage changes for either protein. After five PEs, during which exchange of larger plasma volumes was performed (86%), the percentage change of PC was greater than after the 50 percent exchange (38 +/- 22 vs. 55 +/- 24). To study postexchange recovery, PC was also measured serially for up to 24 hours after eight PEs (50% exchange). At 24 hours postexchange, PC levels did not differ significantly from pre-exchange levels. This study demonstrates that decreases in PC are in proportion to the volume of plasma exchanged during PE. However, PC levels returned to normal within 24 hours after PE, so that any hemostatic imbalance induced by low PC should be transient.