Levels of free activated protein C are a measure of the activation of
the protein C pathway in vivo. The aim of this study was to establish
if the protein C pathway is triggered in familial thrombophilia and if
activated protein C levels correlate with type of defect or symptoms.
We measured activated protein C in 133 patients with a deficiency of
antithrombin (n = 31), protein C (n = 24) or protein S (n = 27) or wit
h resistance to activated protein C (n = 51). Levels of activated prot
ein C were evaluated also in 97 healthy individuals. Results indicate
that the levels of activated protein C are higher in patients who have
experienced a thrombotic event than in patients who have not and that
71% of patients with levels of activated protein C above the normal r
eference range had had a venous thromboembolic event. We conclude that
the protein C pathway is triggered in patients with thrombophilia and
that in symptomatic patients, activated protein C levels are increase
d and may reflect heightened coagulation activation and scavenging thr
ough the protein C pathway.