Summary
Resistance to activated protein C (APC) has been recently identified as a common abnormality
of the clotting system that significantly increases the risk of venous thromboembolism.
The distribution of plasma response to APC in the general population and the variables
potentially influencing it are however unknown. In this study, we analyzed the data
from the first 4,000 subjects enrolled in the Vicenza Thrombophilia and Atherosclerosis
(VITA) Project to identify the demographic and laboratory variables affecting the
plasma response to APC. Plasma response to APC, expressed as APC-ratio, was significantly
influenced not only by the presence of the FV Leiden mutation but also by the aPTT
ratio, triglycerides, fibrinogen and cholesterol level and by pill use, ABO blood
group, gender, smoke, body-mass index and age. The effect of these variables was independent
of the presence of the FV Leiden mutation, and adjustment for their effect improved
the discriminating efficiency of the APC-ratio for the presence of the FV Leiden mutation.
Notwithstanding adjustment, the APC ratio was unsuitable for screening purposes in
the general population (positive predictive value 82.7%).
