**4. Conclusions**

COVID-19 is associated with a hypercoagulable state with acute inflammatory changes. Fibrinogen and D-dimer are increased, with a typical mild prolongation of prothrombin time (PT) and modest thrombocytopenia. The pathogenesis of these abnormalities is not fully understood, and there may be many other related factors contributing to the acute inflammatory response to the disease. Routine thromboprophylactic medication is not recommended in outpatients. For thromboprophylaxis in hospitalised patients with COVID-19, prophylactic antithrombotic dosing with low-molecular-weight heparin is recommended in both moderately and critically ill patients. There may be a subgroup of patients with moderate disease where heparin at therapeutic doses could be beneficial in reducing the need for organ support and death; however, further studies are needed to precisely define this subgroup of patients due to heterogeneity of results.

In critically ill patients, randomised trials with intensive dosing have shown no benefit, but an increased risk of bleeding.
