Active PAI-1 as marker for venous thromboembolism: case-control study using a comprehensive panel of PAI-1 and TAFI assays.

Background: Both activated Thrombin Activatable Fibrinolysis Inhibitor (TAFI) and active Plasminogen Activator Inhibitor-1 (PAI-1) attenuate fibrinolysis and may therefore contribute to the pathophysiology of Venous ThromboEmbolism (VTE). Whether increased TAFI and/or PAI-1 concentrations are associated with VTE is unclear.

Objective: To study an association of impaired fibrinolysis and VTE using a comprehensive panel of in-house developed assays measuring intact TAFI, activation peptide of TAFI (AP-TAFI), PAI-1 antigen, endogenous PAI-1:t-PA complex (PAI-1:t-PA) and active PAI-1 levels in 102 VTE patients and in 113 healthy controls (HC).

Results: Active PAI-1 was significantly higher in VTE patients compared to HC (20.9 [9.6-37.8] ng/ml vs. 6.2 [3.5-9.7] ng/ml, respectively). Active PAI-1 was the best discriminator with an area under the ROC curve and 95% confidence interval (AUROC [95%CI]) of 0.84 [0.79-0.90] compared to 0.75 [0.68-0.72] for PAI-1:t-PA, 0.65 [0.58-0.73] for PAI-1 antigen, 0.62 [0.54-0.69] for AP-TAFI and 0.51 [0.44-0.59] for intact TAFI. Using ROC analysis, we defined an optimal cut-off of 12.8 ng/ml for active PAI-1, with corresponding sensitivity of 71 [61-79] % and specificity of 89 [82-94] %. A lack of association with the time between VTE event and sample collection or with the intake of anticoagulant treatment suggests that active PAI-1 levels are sustainable high in VTE patients.

Conclusions: This case-control study emphasizes the clinical importance of measuring active PAI-1 instead of PAI-1 antigen and identifies active PAI-1 as a potential marker of VTE. Prognostic studies will need to address the clinical significance of active PAI-1 as biomarker.