As more data has become available, the landscape of managing patients with COVID-19 continues to change. This article presents a brief summary of current information regarding COVID-19 infection and its link to thrombosis.

Acute medical illness, such as COVID-19, and hospitalisation confer a greater risk of venous thromboembolism (VTE)1.

Coagulopathy in COVID-19 patients appears to be associated with poor prognosis, an effect common in patients with sepsis2.

Pathogenesis of thrombosis in COVID-19 patients:

COVID-19 infection causes the dysfunction of endothelial cells which in turn results in excessive thrombin generation and cessation of fibrinolysis1. This induces a hypercoagulable state exacerbated by factors related to hospitalisation, including stasis1. Disseminated intravascular coagulopathy (DIC) is reported to occur in most COVID-19 deaths likely as a result of sepsis3.

Severe COVID-19 appears to induce hypoxia which may result in the formation of microthromboses in the small pulmonary blood vessels2.

Patient management:

The International Society of Thrombosis and Haemostasis recommends testing D-dimers, prothrombin time, and platelet count (from most to least important) in patients presenting with COVID-19 infection2. These factors appear to be predictors for mortality in COVID-19 patients. D-dimer and mild thrombocytopenia appear to be the most consistent haemostatic abnormalities and confer a higher risk of requiring ICU admission and mechanical ventilation2. Prothrombin time, thrombin time, and international normalised ratio (INR) are less reliably associated with disease severity4.

Some expert consensus recommends the use of anticoagulants such as low-molecular weight heparin (LMWH) in the treatment of severe COVID-19, though the efficacy has not been sufficiently validated1. The ISTH’s latest interim guidance recommends a prophylactic dose of LMWH be started on all patients presenting with COVID-19 infection, especially those also presenting with markedly increased D-dimer and prothrombin time, a platelet count under 100 x 109/L, and fibrinogen under 2.0 g/L2. Contraindications to this recommendation include active bleeding, or a platelet count less than 25 x 109/L, and monitoring is advised in severe renal impairment2.

The Thrombosis and Haemostasis Society of Australia and New Zealand (THANZ) recommends expert haematologist review of LMWH treatment if the patient has a low platelet count of under 50 x 109/L, a fibrinogen level under 1.0 g/L, or creatinine clearance under 30 mL/min (severe renal impairment)5. Further, they recommend the consideration of continued LMWH or direct oral anticoagulant (DOAC) treatment post-discharge4.


  1. Tang et al. 2020. Anticoagulant treatment is associated with decreased mortality in severe coronavirus disease 2019 patients with coagulopathy. Journal of Thrombosis and Haemostasis.
  2. Thachil et al. 2020. ISTH interim guidance on recognition and management of coagulopathy in COVID-19. Journal of Thrombosis and Haemostasis.
  3. Tang et al. 2020. Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia. Journal of Thrombosis and Haemostasis.
  4. Bikdeli, B. et al. 2020. COVID-19 and Thrombotic or Thromboembolic Disease: Implications for Prevention, Antithrombotic Therapy, and Follow-up.
  5. Thromboprophylaxis and thrombosis in COVID 19 infected patients admitted to hospital. THANZ 2020. Available from: