Risk of first venous thrombosis by comparing different thrombin generation assay conditions: results from the MEGA case-control study.

Hypercoagulability is a risk factor for venous thromboembolism (VTE). Thrombin generation (TG) is a global coagulation assay that measures an individual's clotting tendency. We hypothesise that slow-onset TG (achieved by using a low procoagulant stimulus or an inhibitor of coagulation) is the optimal responsive TG method for detecting hypercoagulability.This study aimed to compare different TG assay conditions with respect to VTE risk and assess the risk of the first VTE. Basal TG at low tissue factor (TF) concentration and high TF concentration in the presence and absence of activated protein C (APC) were measured in plasma samples from 2,081 patients with first VTE and 2,908 healthy controls from the Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis (MEGA) study. TG parameters and normalised activated protein C sensitivity ratio (nAPCsr) were categorised into quartiles as measured in the controls. We calculated odds ratios (ORs) with 95% confidence intervals (CIs) of the first VTE for different TG categories. Under all assay conditions the thrombin peak height was associated with VTE risk: peak height of >75th percentile, at low TF OR 6.8 (95% CI 5.5-8.3), at high TF, OR 3.0 (95% CI 2.5-3.6), and at high TF + APC, OR 3.8 (95% CI 3.2-4.5), all compared with a peak height of <25th percentile obtained in controls. An increased nAPCsr (higher resistance to APC) was also associated with VTE risk, OR 3.4 (95% CI 2.8-4.1). Increased TG is associated with the risk of first VTE, particularly when triggered with a low procoagulant stimulus.