Tissue factor activity is increased in a combined platelet and microparticle sample from cancer patients

Background: Cancer patients have an increased risk of thrombosis. Tissue factor (TF) antigen and TF activity associated with microparticles in plasma are elevated in patients with various types of cancer. Of these two measurements, TF activity is considered superior to TF antigen levels because the activity more closely reflects the ability of TF to initiate coagulation. Recent studies showed that platelets also express TF. Objective: To determine the level of TF activity associated with a combined platelet and microparticle sample from cancer patients (n = 20) and healthy individuals (n = 23). Methods: TF activity was measured using a two step chromogenic assay and soluble P-selectin was measured by ELISA in healthy controls and metastatic cancer patients. Results: We determined the composition of a combined platelet and microparticle sample. The sample consisted of platelets, large microparticles (30-200 nm) and membrane debris. We compared the TF activity of a combined platelet and microparticle sample from cancer patients with that from healthy individuals. We found that TF activity in a combined platelet and microparticle sample from cancer patients was higher than in samples from healthy individuals (21.5 +/- 12.3 pM (n= 20) versus 8.6 +/- 6.8 pM (n=23), mean +/- SD, p<0.001). Cancer patients also had a higher level of soluble P-selectin compared with controls (18.9 +/- 5.5 ng/mL versus 13.2 +/- 2.3 ng/mL, p<0.001). Conclusion: This study indicates that measurement of TF activity in a combined platelet and microparticle sample can be used as a simple assay to determine the level of circulating TF (C) 2008 Elsevier Ltd. All rights reserved.