Measurement of a newly developed thrombomodulin addition activated partialthromboplastin time assay in patients with deep venous thrombosis

We developed a simple assay using rabbit thrombomodulin (TM) based on an ac tivated partial thromboplastin time method, which detected the response to TM in plasma coagulation. We call it thrombomodulin addition clotting time (TACT). The anticoagulant response to TM was calculated by dividing the clo tting time with TM by the clotting time with buffer solution. Results were expressed as TACT ratio, which indicates the degree of inhibition of plasma clotting by TM. Using this assay, we measured the TACT ratio in 80 patient s with deep-vein thrombosis (DVT) and in 126 controls matched to the patien ts according to age and sex. A significant difference in the TACT ratio was observed between patients with DVT (mean 1.874) and controls (mean 1.956) (p < 0.001). Twenty-three patients (29%) had TACT ratios below the 10th per centile (1.757) of distribution of control subjects (odds ratio: 3.5; 95% c onfidence interval (CI): 1.7-7.2). After excluding subjects with a deficien cy of protein C, protein S and antithrombin ill, we found an odds ratio for DVT of 3.4 (95% CI: 1.6-7.2). These data suggest that natural anticoagulan t deficiencies do not influence the TACT ratio, and our case-control study may show that the plasma of patients with DVT has a low response to TM. Cop yright (C) 2001 S. Karger AG, Basel.