Summary
A simple and fast method for the quantitative determination of protein C activity
in plasma is here described. The first step consists in the conversion of protein
C in the test sample into activated protein C by means of an activator isolated from
Southern Copperhead venom. Subsequently, the degradation of factor Va, in presence
of protein C-deficient plasma, is measured by the prolongation of the prothrombin
time which is proportional to the amount of protein C in the sample. The dose-response
curve showed a linear relationship from 6 to 150% protein C activity and the inter-
and intra-assay reproducibility was 3.5% and 5.6% respectively. In normal subjects,
a mean of protein C level of 98 ± 15% of normal pooled plasma was found. Comparison
with the anticoagulant assay in samples of patients with oral anticoagulant, liver
cirrhosis, disseminated intravascular coagulation and severe preeclampsia revealed
an excellent correlation (r = 0.94, p <0.001). Also, a similar correlation (r = 0.93, p <0.001) existed between amidolytic assay and the method here proposed for all the
samples studied without including the oral anticoagulant group. These results allowed
us to infer that this method evaluates the ability of protein C to interact with protein
S, phospholipids, calcium ions and factor Va.
