Key points > COVID-19 is associated with a hypercoagulable state with increased VTE rate. > COVID-19 patients frequently have very high von Willebrand factor (vWF) and factor VIIIc levels that are comparable to those seen in ICU patients with severe sepsis. > Further studies are needed urgently to evaluate the use of vWF as a pragmatic measure to stratify thrombotic risk in COVID-19.

Background A possible association between COVID-19 infection and thrombosis, either as a direct consequence of the virus or as a complication of inflammation, is emerging in the literature. Data on the incidence of venous thromboembolism (VTE) are extremely limited. Methods We describe three cases of thromboembolism refractory to heparin treatment, the incidence of VTE in an inpatient cohort, and a case-control study to identify risk factors associated with VTE. Results We identified 274 confirmed (208) or probable (66) COVID-19 patients. 21 (7.7%) were diagnosed with VTE. D-dimer was elevated in both cases (confirmed VTE) and controls (no confirmed VTE) but higher levels were seen in confirmed VTE cases (4.1 vs 1.2 µg/mL, p<0.001). Conclusion Incidence of VTE is high in patients hospitalised with COVID-19. Urgent clinical trials are needed to evaluate the

Coagulopathy (Tang , et al 2020) and a prothrombotic diathesis with high D‐dimer and fibrinogen levels (Al‐Samkari , et al 2020) are associated with coronavirus disease 2019 (COVID‐19) caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). Extensive thrombosis in small vessels and the microvasculature in lungs and extrapulmonary organs has been confirmed histologically (Zhang et al 2020). Early studies showed that the venous thromboembolism (VTE) incidence in hospitalised COVID‐19 patients can be as high as 25% (Songping , et al 2020), and more recent studies have indicated this can be expanded to other macrovascular thrombotic complications, such as a higher than expected prevalence of pulmonary emboli in patients with COVID‐19 (Klok , et al 2020, Stoneham , et al ).