With reports of cardiovascular complications such as heart attack and stroke on the rise, researchers from Sweden, Finland, and the U.K. conducted a large study to help determine the risks of post-COVID deep-vein thrombosis (DVT), pulmonary embolism (PE)–or clotting in one or more lung arteries–and the risk of bleeding from blood-thinning therapies.*

What the Researchers Did

The research team analyzed 1,057,147 Swedish citizens, average age roughly 40 years, who tested positive for SARS-CoV-2 between February 1, 2020 and May 25, 2020. Each participant was matched by age, sex, and county of residence to 4,076,342 participants acting as controls.

In a second study, each COVID patient’s own rates of complications before and after infection were compared.

What They Found

The researchers found an increase in risk for DVT, PE, and bleeding after COVID-19.

COVID-19 and DVT risk:

• In the self-controlled case series, 1,761 participants had their first DVT.
• Compared to the control period before COVID infection, incidence rose slightly through week 2 after infection and then sharply through day 70.
• In the first 3 months following infection, DVT rose generally in accordance with age.
• While sex had no real impact on the link between COVID-19 and DVT, severe COVID-19 increased DVT risk.
• DVT risk in the 30-day follow-up period was similar in the self-controlled and matched cohort studies.

The results remained significant after factoring concurrent illness, cancer, surgery, and long-term use of blood-thinning therapies, which did not lower DVT risk.

COVID-19 and PE risk

• In the self-controlled case series, 3,267 participants had their first PE event (including 1,761 patients and 171 controls during the first 30 days). 
• In the first 3 months post-COVID, there were more new cases of PE in men versus women, as well as in those 50-70 years old.
• PE risk was higher in patients who had severe COVID-19.
• Patients who had more severe COVID-19 had a higher risk of PE, especially those hospitalized and admitted to intensive care.
• For all PE events 2,226 happened in COVID patients and 444 in controls after 30 days.

The results remained significant after adjusting for concurrent illness, cancer, surgery, and long-term use of blood-thinning therapies, which did protect against PE.

COVID-19 and bleeding risk

• In the self-controlled case series, 7,927 participants had their first related bleeding event.
• New cases rose slightly through week 2 after infection, then sharply through day 60.
• In the first 2 months post-COVID, higher bleeding incidence was seen in men versus women, and rose with advancing age.
• Bleeding risk was higher in patients who had severe COVID-19; no increased bleeding risk was seen in mild cases.
• Over the first 30 days post-COVID, first-time bleeding was seen in 1,002 COVID patients, mostly with severe disease, and in 1,292 controls.

The results remained significant after factoring in concurrent illness, cancer, surgery, and long-term use of blood-thinning therapies, which was linked to elevated bleeding risk.

What It Means

Overall, risk of complications increased after SARS-CoV-2 infection. 

• DVT risk increased up to 3 months post-COVID, 
• PE up to 6 months, and 
• Bleeding up to 2 months. 

The study also showed a higher risk of these complications in patients with concurrent illnesses, and those who had more severe cases of COVID-19. Despite the study’s limitations, such as the potential for inaccurate or incomplete data within a patient registry, the authors say their results have “major policy implications.” 

“Our findings arguably support thromboprophylaxis to avoid thrombotic events,” they wrote, “especially for high risk patients, and strengthens the importance of vaccination against covid-19.” 

They advise that further research is needed to determine whether extending blood-thinning therapy after COVID-19 might be helpful.

*Katsoularis, I., Fonseca-Rodríguez, O., Farrington, P., Jerndal, H., et al. (2022, April 6). Risks of deep vein thrombosis, pulmonary embolism, and bleeding after covid-19: nationwide self-controlled case series and matched cohort study. BMJ, 377(e069590). https://www.bmj.com/content/377/bmj-2021-069590