In Vivo and Ex Vivo Thrombin Generation in Noncomorbid Patients with Suspected Deep Venous Thrombosis

Abstract

Thrombin generation in vivo can be assessed by measuring prothrombin fragment 1+2 (F1+2) and D-dimer. The F1+2 fragment is generated during prothrombin conversion to thrombin and thus reflects thrombin generation. Degradation of cross-linked fibrin produces D-dimer, which reflects both ongoing coagulation and blood clot dissolution. Ex vivo, thrombin generation can be assessed by the thrombin generation assay, in which the endogenous thrombin potential (ETP) reflects the total enzymatic activity of thrombin. The aim was to compare thrombin generation in vivo and ex vivo in patients with suspected deep venous thrombosis (DVT). Patients with clinically suspected DVT and without known comorbidities or taking anticoagulants were included. Blood samples were collected before examination with compression ultrasound of the lower extremities. In vivo parameters were analyzed with commercially available enzyme-linked immunosorbent assay. The ETP was measured by the calibrated automated thrombogram assay. Differences between DVT-negative and DVT-positive patients were assessed with the Mann-Whitney U test. The area under the receiver operating characteristic curve was used to determine the overall performance of the measured parameters. The median age of the 253 patients (111 male) was 54 (range, 18-93) years. The DVT was confirmed by imaging in 51 (20%) patients. There was no significant age difference between the DVT-negative and DVT-positive groups (P = .810). The DVT-positive group had more men (P < .001). Levels of the measured parameters in the DVT-negative and DVT-positive groups are shown in the Fig. A cohort without comorbidities or taking anticoagulants was selected in an attempt to show the isolated impact of lower extremity thrombosis on thrombin generation measured both in vivo and ex vivo. Levels of in vivo thrombin generation were increased in patients diagnosed with DVT vs those without. However, ex vivo ETP levels did not differ. Increased ETP levels are associated with increased risk of venous thromboembolism. Our observed discrepancy between in vivo and ex vivo parameters might be explained by a consumption of potential to generate thrombin ex vivo after an event that generates thrombin in vivo. Patients with high levels of in vivo thrombin generation parameters should thus have lower levels of ETP. A ratio of the in vivo biomarkers and ETP was therefore expected to have higher overall performance to diagnose DVT than F1+2 and D-dimer alone, which was not observed. The DVT increased the levels of F1+2 and D-dimer, but levels of ex vivo thrombin generation measured by ETP were not different from those without DVT.