Inhibition of tissue factor pathway inhibitor increases the sensitivity of thrombin generation assay to procoagulant microvesicles

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Patients with cancer have a seven-fold to 10-fold increased risk of developing venous thromboembolism (VTE). Circulating microvesicles could be a predictive biomarker for VTE in cancer. Thrombin generation assay (TGA) is a useful technique to detect procoagulant activity of microvesicles. However, TGA suffers from a lack of sensitivity due to the presence of tissue factor pathway inhibitor (TFPI) in plasma. The aim of the study was to improve the sensitivity of TGA to tissue factor by limiting the interference of TFPI. Serial dilutions of MDA-MB231 cells were incubated for 45 min at 37°C to generate microvesicles. Samples were then centrifuged and supernatants that contain microvesicles were used for TGA. Normal pooled plasma was incubated with inhibitor of TFPI or was diluted twice to decrease plasma level of TFPI. Lagtime was used as a surrogate marker of TGA to detect procoagulant activity of microvesicles. Inhibition of TFPI decreased twice the cell concentration needed for a significant reduction of lagtime and decreased 2.4-fold the intraassay variability. Plasma dilution had no impact on the TGA sensitivity when TGA was triggered by microvesicles derived from MDA-MB-231. Thrombin generation is a very sensitive method to study the procoagulant activity of tissue factor bearing microvesicles. The sensitivity can be increased by inhibition of TFPI with specific monoclonal antibody against its Kunitz domain I. A two times plasma dilution is an interesting cheaper alternative to study the procoagulant activity of microvesicles by TGA with a good sensitivity, especially when low plasma quantities are available.