Tissue factor and its measurement in whole blood, plasma, and microparticles

Tissue factor (TF) is a transmembrane protein that initiates coagulation following contact with factor VII/VIIa. Recent experimental evidence, in particular from animal models, suggests an important role for circulating TF in thrombosis. This has led to a growing interest in the measurement of TF in whole blood and in cell-free plasma, where functionally active TF is carried on cell-derived microparticles. In this review, we address the range of assays for measuring circulating TF antigen and activity that have been published. We comment on some of the crucial preanalytical and analytical variables that influence the results and their interpretation.