BackgroundTissue factor (TF) is essential for hemostasis. TF-expressing extracellular vesicles (TF+EVs) are released in pathological conditions, such as trauma and cancer, and are linked to thrombosis. Detection of TF+EV antigenically in plasma is challenging due to their low concentration but may be of clinical utility.ObjectivesWe hypthesised that ExoView can allow for direct measurement of TF+EV in plasma, antigenically.MethodsWe utilized the anti-TF monoclonal antibody 5G9 to capture TF EV onto specialized ExoView chips. This was combined with fluorescent TF+EV detection using anti-TF monoclonal antibody IIID8-AF647. We measured tumor cell-derived (BxPC-3) TF+EV and TF+EVs from plasma derived from whole blood with or without lipopolysaccharide (LPS) stimulation. We used this system to analyze TF+EVs in 2 relevant clinical cohorts: trauma and ovarian cancer. We compared ExoView results with an EV TF activity assay.ResultsBxPC-3-derived TF+EVs were identified with ExoView using 5G9 capture with IIID8-AF647 detection. 5G9 capture with IIID8-AF647 detection was significantly higher in LPS+ samples than in LPS samples and correlated with EV TF activity (R2= 0.28). Trauma patient samples had higher levels of EV TF activity than healthy controls, but activity did not correlate with TF measurements made by ExoView (R2= 0.15). Samples from patients with ovarian cancer have higher levels of EV TF activity than those from healthy controls, but activity did not correlate with TF measurement by ExoView (R2= 0.0063).ConclusionTF+EV measurement is possible in plasma, but the threshold and potential clinical applicability of ExoView R100, in this context, remain to be established.