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Can COVID-19 cause blood clots?

Is COVID-19 associated with venous thromboembolism?

Medically reviewed by Last updated on April 20, 2020.

Official Answer


Blood clots, or venous thromboembolisms (VTEs) as they are also known, are of growing concern in patients with severe COVID-19. The American Society of Hematology is now referring to the blood clotting-related issues observed in patients with COVID-19, as COVID-19-associated coagulopathy (CAC).

Lab test results show blood clotting issues in COVID-19 patients

When doctors test the blood of patients hospitalized with COVID-19, they find increased levels of fibrinogen and D-dimer in some of these patients, which indicates the presence of CAC or blood clotting issues. Fibrinogen is a protein that is also known as clotting Factor I. It plays a central role in the formation of blood clots. D-dimer is a small protein fragment or fibrin degradation product, which is found in the blood after enzymes break down a blood clot.

Some patients with severe COVID-19 also develop what is classified as disseminated intravascular coagulopathy (DIC). DIC is a rare but serious disorder in which small blood clots can develop throughout the body and it is known to be caused by other infections.

How does COVID-19 cause blood clots?

We know from looking at other infections that they can cause blood clots and that infection-induced blood clots are more likely to be mediated by the inflammation caused by the infectious agent or its products. COVID-19, the disease caused by the new coronavirus SARS-CoV-2, is also known to cause inflammation, including inflammatory cytokine storm. It is thought that the inflammation caused by COVID-19 sets off a chain of events that causes blood clots to develop.

Blood clots in COVID-19 patients associated with a poor prognosis

Analysis of information from 171 patients hospitalized with COVID-19 in China has revealed that in the 53 patients who died, D-dimer levels were clearly elevated (which indicates the body is working to break down blood clots) compared with levels observed in the 118 patients who survived. D-dimer levels became more elevated as the condition of the patients deteriorated.

Significantly higher D-dimer levels were also observed in the 21 patients who died in a study conducted in 183 patients with COVID-19 in China. A total of 71.4% of the patients who died also developed DIC, compared with only 0.6% of the patients who survived.

Other reports also note that blood clots in the form of pulmonary embolism (PE) and venous thromboembolism (VTE) are seen in severe cases of COVID-19.

Treatments for COVID-19 patients with blood clots

Researchers are continuing to investigate how best to treat patients with COVID-19. In the meantime they are using their clinical experience to determine the best way to treat and prevent blood clots in patients with COVID-19. Existing anticoagulant medications, such as low molecular weight heparin, are being used.

Clinical trials are also being undertaken to investigate drugs with anti-inflammatory potential in patients with COVID-19. These drugs may help to prevent the inflammation that contributes to the development of blood clots in severe cases of COVID-19.

  • American Society of Hematology. COVID-19 Resources. COVID-19 and Coagulopathy: Frequently Asked Questions. April 14, 2020. [Accessed April 20, 2020]. Available online at:
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  • Zhou F, Yu T, Du R, et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study. Lancet. 395(10229), P1054-1062. March 28, 2020. DOI:
  • Magro C, Mulvey JJ, Berlin D, Nuovo G, Salvatore S, Harp J, Baxter-Stoltzfus A, Laurence J. Complement associated microvascular injury and thrombosis in the pathogenesis of severe COVID-19 infection: A report of five cases.  Epub ahead of print. [Accessed April 20, 2020]. Transl Res. April 25, 2020. S1931-5244(20)30070-0. doi: 10.1016/j.trsl.2020.04.007.
  • Tang N, Li D, Wang X, Sun Z. Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia. J Thromb Haemost. 2020 Apr;18(4):844-847. doi: 10.1111/jth.14768.
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