Normal Soluble Fibrin Levels Suggest a Low Probability of Pulmonary Embolism in Patients with Deep Vein Thrombosis

Pulmonary embolism (PE) and deep vein thrombosis (DVT) are part of venous thromboembolism (VTE). Since PE can be fatal, early diagnosis in DVT patients is crucial. Diagnosing PE is often difficult due to non-specific symptoms. D-dimer testing is commonly used to exclude PE but is less effective in DVT patients because they generally have elevated D-dimer levels. Additionally, imaging, such as contrast-enhanced CT, may not be feasible for all patients. This study focused on soluble fibrin (SF), an early marker of thrombus formation that reflects thrombin generation, instead of D-dimer. Among 133 acute DVT patients who underwent imaging, 71 had PE (PE group), and 62 did not (no-PE group). All patients, except one patient in the no-PE group, exhibited elevated D-dimer levels, with no significant difference in the proportion of patients with normal D-dimer levels between the groups (P = .466). In contrast, 26 of 62 patients in the no-PE group had normal SF levels, while only 5 of 71 in the PE group showed normal SF levels. The proportion of patients with normal SF was significantly lower in the PE group (P < .0001). Multivariate analysis indicated that normal SF was the only independent factor in excluding PE (OR 8.86, 95%CI 2.94-26.7, P = .0001). These findings suggest that DVT patients with normal SF levels are unlikely to have PE. SF might be more useful than D-dimer in excluding PE and could help reduce unnecessary imaging in DVT patients when used alongside standard diagnostic methods.