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Can COVID-19 cause blood clots?

Medically reviewed by Last updated on April 10, 2023.

Is COVID-19 associated with venous thromboembolism?

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:
  • Beristain-Covarrubias N, Perez-Toledo M, Thomas MR, et al. Understanding Infection-Induced Thrombosis: Lessons Learned From Animal Models. Front. Immunol. November 5, 2019.
  • 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.
  • Bikdeli B, Madhavan MV, Jimenez D, et al. COVID-19 and Thrombotic or Thromboembolic Disease: Implications for Prevention, Antithrombotic Therapy, and Follow-up. JACC Pre-proof April 2020. [Accessed April 20, 2020]. DOI: 10.1016/j.jacc.2020.04.031.
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