Introduction
Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Besides respiratory failure, COVID-19 also has high rates of thromboembolic complications as seen in multiple retrospective studies.1–3 In accordance, autopsy studies showed high incidences of macro- and microemboli in patients who were infected by SARS-CoV-2.4,5 These thrombotic complications could be responsible for a significant part of the morbidity and mortality seen in COVID-19 patients.3 The exact underlying pathophysiology of COVID-19 related thrombotic complications remains unknown, but excessive inflammation, hypoxia, immobilization, thrombotic microangiopathy, diffuse intravascular coagulation, and complement activation most likely play a role.6 Moreover, low-molecular-weight heparin (LMWH) thromboprophylaxis seems to decrease mortality in patients with COVID-19.15
Based on these data, guidelines recommend administration of prophylactic LMWH for all hospitalized patients with COVID-19.16,17However, recent reports show that despite the use of apparently adequate thrombosis prophylaxis, the incidence of venous thromboembolism (VTE) in COVID-19 patients who were admitted to a hospital ward appears to be much higher compared to patients with other infectious diseases.2,18,19 Therefore, it was suggested that in COVID-19 patients increased intensity thromboprophylaxis or therapeutic anticoagulation should be considered.16,21,22 However, studies that address the effect of therapeutic anticoagulation on clinical outcomes show conflicting results, and often compare very heterogeneous cohorts that lack statistical power to draw firm conclusions.23–27 The aim of this study is to investigate the beneficial effect of therapeutic anticoagulation used prior to hospitalization on morbidity and mortality in a large cohort of hospitalized COVID-19 patients.