Summary
Activated protein C reduces thrombin generation by inactivating factors V and VIII
in the presence of protein S. This prompted us to develop an assay which would allow
specific exploration of this reaction. The total amount of thrombin formed in plasma
after activation by tissue factor and phospholipids was reduced by adding thrombomodulin.
This addition allowed protein C to be activated by endogenous thrombin. The inhibition
of thrombin generation (ITG) due to protein C activation could be measured by comparing
thrombin formation in the presence and in the absence of thrombomodulin. ITG increased
with both protein C and protein S concentrations. Normal values of ITG expressed as
a percentage were between 40 and 65% and were not influenced by age or sex. ITG increased
in patients under heparin therapy, decreased in patients under oral anticoagulant
therapy and was decreased in women using oral contraceptives. This method could be
used for screening patients for protein C and protein S deficiencies.