Summary
Tissue factor (TF) is present in small quantities in normal blood and is reported
to be elevated in arterial and venous thrombosis. Patients undergoing total knee arthoplasty
(TKA) are at high risk of post-operative venous thromboembolism (VTE). To evaluate
the possible contribution of elevated blood TF to VTE risk, we performed serial studies
of peripheral blood mononuclear cell (PBMC) functional TF procoagulant activity (PCA)
in 19 patients after TKA. PBMC and platelet TF PCA were measured by a functional,
clot-based assay following decryption with a calcium ionophore. Plasma TF antigen
levels were measured by ELISA. All subjects received chemoprophylaxis and none had
VTE. After TKA total TF PCA of PBMC was elevated in 19 of 19 subjects. The peak increase
above preoperative levels was 1. 1–13.6 fold (>two-fold in 58% and >three-fold in
42%). Median TF PCA of PBMC was not elevated following tourniquet removal, but it
was significantly elevated on postoperative days 1 and 2. Thereafter, it decreased
to near preoperative values at day 6. Neither platelet TF PCA nor plasma TF antigen
levels increased significantly. Since the PBMC count did not rise, the increase in
TF PCA was attributable to cell synthesis. The increase in blood TF PCA preceded the
median time of diagnosis of venous thromboembolism after TKA established previously.
These observations indicate a) TKA stimulates synthesis of encrypted PBMC TF PCA which
is likely to contribute to the pathophysiology of VTE; b) TF antigen is not a reliable
indicator of TF PCA.
Keywords
Tissue factor - knee arthroplasty - leukocyte procoagulant activity - blood platelets
