Detection of endogenous tissue factor levels in plasma using the calibrated automated thrombogram assay

Abstract

Background: The calibrated automated thrombogram (CAT) assay measures thrombin generation in plasma.

Objective: Use the CAT assay to detect endogenous tissue factor (TF) in recalcified platelet-rich plasma (PRP) and platelet-free plasma (PFP).

Methods: Blood from healthy volunteers was collected into citrate and incubated at 37 degrees C with or without lipopolysaccharide (LPS) for 5 hours. PRP and PFP were prepared and clotting was initiated by recalcification. Thrombin generation was measured using the CAT assay.

Results: The lag time (LT) was significantly shortened in PRP prepared from LPS-treated blood compared with untreated blood (10+/-3 min versus 20+/-6 min), and this change was reversed by the addition of inactivated human factor VIIa. LPS stimulation did not change the peak thrombin. Similar results were observed in PFP (21+/-4 min versus 35+/-5 min). LPS stimulation also significantly reduced the LT of PRP and PFP derived from blood containing citrate and a factor XIIa inhibitor. Finally, a low concentration of exogenous TF shortened the LT of PFP prepared from unstimulated, citrated blood without affecting the peak thrombin.

Conclusion: Changes in LT in the CAT assay can be used to monitor levels of endogenous TF in citrated plasma.