Summary
As specific assays used to identify defects in the protein C (PC) anticoagulant pathway
are laborious and expensive, we describe here a global test to screen for these defects.
This assay is expressed as the ratio of two activated partial thomboplastin times,
one in the absence and one in the presence of 0,125 U/ml of the PC activator of Agkistrodon
contortrix venom (ACV). Eight of the 168 healthy volunteers of the control group exhibited
an ACV ratio below the lower normal limit of 3.37 [6 subjects with the mutation Arg
506 to Gin in their factor V gene (FV R506Q) and one with PS deficiency]. 128 patients
who have had at least one episode of deep-vein thrombosis were retrospectively studied.
All patients carrying FV Q506R (n = 48), PC deficiency (n = 14) or combined defects,
i. e. FV Q506R and PC deficiency (n = 4) or FV Q506R and PS deficiency (n = 3), had
ACV ratios < 3.37. PS deficient plasmas (n = 20) exhibited ACV ratios which overlapped
normal range. ACV ratios of one out of seven patients with antithrombin deficiency,
and 10% of patients without identified defect in the PC anticoagulant pathway (n =
30) were < 3.37. An ACV ratio raised to 3.70 could lead to a test identifying all
patients with a defect in the PC anticoagulant pathway.
