Role of Fibrin Monomer Complex in Coronavirus Disease 2019 for Venous Thromboembolism and the Prognosis

Objective Venous thromboembolism (VTE) is a common complication of severe coronavirus disease 2019 (COVID-19) and is associated with its prognosis. The fibrin monomer complex (FMC), a marker of thrombin generation, is reportedly useful in diagnosing acute thrombosis. To date, there has been only one report on FMC in COVID-19, and the usefulness of FMC in COVID-19 is unknown. We therefore evaluated the frequency of VTE in non-intensive-care unit COVID-19 patients in Japan and determine the clinical utility of FMC in COVID-19.Methods This was a single-center retrospective study. Laboratory test results and outcomes (thrombosis and severe progression of COVID-19) were obtained via medical record review. We assessed the relationship be-tween FMC and VTE incidence and evaluated the association between elevated FMC levels and severe progression of COVID-19.Patients This study included 247 patients with COVID-19 who were hospitalized between December 2020 and September 2021 and had had their levels of D-dimer and FMC measured.Results Of the 247 included patients, 3 (1.2%) developed VTE. All three had elevated FMC levels on admission; however, the D-dimer level was not elevated in one case on admission. The FMC level was significantly higher in the group with severe COVID-19 progression than in the group without severe progression. A multivariate analysis showed that severe progression was associated with elevated FMC levels (odds ratio, 7.40; 95% confidence interval, 2.63-22.98; p<0.001).Conclusion FMC can be useful for diagnosing VTE in the acute phase of COVID-19. Elevated FMC was found to be associated with severity on admission and severe progression.