Pre-Analytical and Analytical Variables Affecting the Measurement of Plasma-Derived Microparticle Tissue Factor Activity

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Introduction: Elevated levels of tissue factor positive (TF +) microparticles (MPs) are observed in plasma from a variety of patients with an increased risk of thrombosis. We and others have described the measurement of TF activity in MPs isolated from plasma. The aim of this study was to investigate the effects of pre-analytical and analytical variables on TF activity of MPs isolated from blood of healthy volunteers either untreated or treated ex vivo with bacterial lipopolysaccharide. Materials and methods: We evaluated the following parameters: use of different centrifugation speeds to isolate the MPs; comparison of TF activity of MPs isolated from platelet poor plasma versus platelet free plasma; effect of freeze/thaw on MP TF activity; and comparison of the MP TF activity assay with the measurement of TF protein by ELISA or flow cytometry. Results: MPs prepared from platelet poor plasma by centrifugation at 20,000 × g or 100,000 × g for 15 minutes had similar levels of TF activity. However, significantly less TF activity was found in MPs isolated from platelet free plasma compared with platelet poor plasma. Interestingly, freeze/thawing of the plasma showed donor to donor variation in MP TF activity, with a moderate increase in some individuals. Conclusion: TF + MPs can be quantitatively isolated from platelet poor or platelet free plasma by centrifugation at 20,000 × g for 15 minutes. Measurement of MP TF activity in plasma may be used to detect a prothrombotic state in patients with various diseases.