Abstract
Changes in protein C activity, protein C antigen, Vitamin K-dependent coagulation factors (II, VII, IX, X) and protein C induced vitamin K abscense of factor II (PIVKA-II) were investigated in 30 patients treated with Warfarin for long periods. Those included 23 patients with prosthetic heart valves and 7 patients reconstructed peripheral vessels. Protein C activity was measured by rapid assays. amidolytic and clotting time assays using a protein C activator (PROTAC®) from the venom of Agkistrodon contortrix. Protein C levels measured by amidolytic assay correlated significantly with the immunological assay (ELISA) (r=0.718, p<0.001), but the clotting time assay gave lower protein C values than the amidolytic and immunological assays. Furthermore, the ratio of protein C activity (clotting time assay) to protein C antigen tended to decrease against the increase in PIVKA-II. The comparison of the three PC assays to thrombotest indicated that highly significant correlation was found between clotting time assay and thrombotest (r=0.483, p<0.01), furthermore, protein C values measured by the clotting time assay correlated with prothrombin activity (r=0.598, p<0.001). However a decrease in the ratio of protein C activity (clotting time assay) to prothrombin activity was observed in three cases with prosthetic heart valves (ratios of 0.25, 0.28, 0.34 and the prothrombin activities of these cases were beyond 30%). These results indicate that the protein C activity measured by clotting time assay evaluates the in vivo function of protein C, and that protein C function as well as prothrombin activity is inhibited in patients on stable oral anticoagulant therapy.
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