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Patient Evidence Summary
Doctor, I have inherited a clotting disorder. Does infection with COVID increase my risk of developing a blood clot?
In people who have inherited the Factor V Leiden mutation or Prothrombin Gene mutation, infection with COVID doubles the risk of developing DVT and PE.
Study highlights
People with COVID infection diagnosed outside of a hospital had 21 times higher risk of developing DVT or PE compared to people not infected with COVID. Vaccination with at least 2 doses of COVID vaccine reduced the risk of developing DVT or PE following COVID infection.
Vaccination with COVID vaccine did not increase the risk of DVT or PE.
Understanding the problem
Infection with COVID increases the risk of developing DVT and PE. This risk is particularly high in people who require admission to hospital. It is less clear if being infected with COVID, but not requiring admission to hospital increases the risk of DVT and PE. Also, it is unclear if additional risk factors such as age, sex or a known clotting disorder, increase the risk of clotting in people who test positive for COVID or received vaccination for COVID.
The Factor V Leiden mutation and Prothrombin Gene mutation are two of the known blood clotting disorders . They are changes (known as mutations) to the genes that control blood clotting proteins. These mutations are inherited from one or both parents and increase the risk of a person developing DVT and PE.
In February 2021, some people who received the AstraZeneca COVID vaccine developed blood clots in unusual locations including the veins around the brain (CVST) and even more rarely, in veins around the intestines or liver. This was an unusual type of blood clotting that was triggered by the immune system. This observation made some people who have inherited blood clotting disorders concerned that being vaccinated against COVID would increase their risk of having another blood clot.
Researchers in this study wanted to know if risk factors such as age, sex or blood clotting disorders, such as Factor V Leiden or Prothrombin Gene mutation, increase the risk of DVT and PE after COVID infection compared to people who do not have these risk factors.
Who? This observational study included 18,818 people from a large UK database who had a positive test for COVID between March 1, 2020 and September 30, 2021 and matched them with 93,179 people who were negative for COVID or had never been tested. People who had a past history of DVT or PE or had taken blood thinners within the previous year, and people who were diagnosed with COVID while in a hospital were excluded.
What? The study compared the risk of developing DVT and PE in people who were confirmed COVID (COVID-positive) versus people who had negative test results for COVID or had never been tested (COVID-negative).
Risk of DVT and PE after COVID infection or after COVID vaccination
Outcomes at 30 days | Group 1 | Group 2 | Results |
|---|---|---|---|
DVT or PE | COVID-positive people | COVID-negative people | COVID-positive people were 21 times more likely to have DVT or PE compared to COVID-negative people |
| DVT or PE | Vaccinated* COVID-positive people | Vaccinated* COVID-negative people | Vaccinated COVID-positive people were 5 times more likely to have DVT or PE compared to vaccinated COVID-negative people |
DVT or PE | Vaccinated* COVID-negative people | Unvaccinated COVID-negative people | Vaccinated COVID-negative people were not more likely than unvaccinated COVID-negative people to have DVT or PE |
| DVT or PE | COVID-positive people with Factor V Leiden or Prothrombin Gene Mutation | COVID-positive people without Factor V Leiden or Prothrombin Gene Mutation | COVID-positive people with FVL or PTGM were 2 times more likely than COVID-positive people without FVL or PTGM to have DVT or PE |
*vaccinated = received two or more doses of COVID vaccine (brand names were not reported); FVL = Factor V Leiden mutation; PTGM= prothrombin gene mutation; FVL = Factor V Leiden mutation; PTGM = Prothrombin Gene Mutation
This Evidence Summary is based on the following article:
Xie J, Prats-Uribe A, Feng Q, et al. Clinical and Genetic Risk Factors for Acute Incident Venous Thromboembolism in Ambulatory Patients With COVID-19. JAMA Intern Med. 2022 Oct 1;182(10):1063-1070. doi: 10.1001/jamainternmed.2022.3858. PubMed
Lori-Ann Linkins, MD, MSc (Clin Epi), FRCPC
Dr. Linkins is an Associate Professor of Medicine (thrombosis) at McMaster University in Hamilton, Canada. She holds a Masters Degree in Health Research Methodology and is a Deputy Editor with the Health Information Research Unit, McMaster. She is Co-Editor of the ACP Journal Club and Co-lead on the CanVECTOR Knowledge Translation Platform.
Published: Monday, December 12, 2022
Please note that the information contained herein is not to be interpreted as an alternative to medical advice from a professional healthcare provider. If you have any questions about any medical matter, you should consult your professional healthcare providers, and should never delay seeking medical advice, disregard medical advice or discontinue medication based on information provided here.
, McMaster University