• By Robert Preidt HealthDay Reporter
• Posted April 7, 2022

Post-COVID Risk for Blood Clot Lasts at Least 6 Months

COVID-19 increases people's risk of dangerous blood clots and bleeding for months after infection, researchers say.

The new findings suggest that COVID-19 is an independent risk factor for deep vein thrombosis, pulmonary embolism and bleeding.

"Our findings arguably support [treatment] to avoid thrombotic events, especially for high-risk patients, and strengthen the importance of vaccination against COVID-19," the study authors concluded in the report published April 6 in the BMJ.

While the added risk of clots and bleeding was known, it was unclear how long it lasted, the researchers noted in a journal news release.

To find out, the investigators compared more than one million people in Sweden who tested positive for COVID-19 between Feb. 1, 2020, and May 25, 2021, and a control group of more than 4 million people who did not have a positive COVID test.

Compared to the control group, COVID-19 patients had a significantly higher risk of deep vein thrombosis, or DVT, (a blood clot in the leg) for up to three months after infection; pulmonary embolism (a blood clot in the lung) for up to six months; and a bleeding event for up to two months.

After accounting for a number of possibly significant factors, the researchers concluded that those with COVID-19 had a five times' higher risk of DVT; a 33-fold higher risk of pulmonary embolism; and a nearly doubled risk of bleeding in the 30 days after infection.

Deep vein thrombosis occurred in 0.04% of COVID-19 patients and 0.01% of control patients. Pulmonary embolism occurred in 0.17% of COVID-19 patients and 0.004% of control patients. And bleeding events occurred in 0.10% of COVID-19 patients and 0.04% of control patients, according to the report.

The risks of blood clots and bleeding were highest in patients whose COVID-19 was more severe, those with other health conditions and those infected during the first wave rather than in the second and third waves. The researchers said that could be explained by improved treatment and vaccine coverage in older patients after the first wave.

Even patients with mild COVID-19 had an increased risk of DVT and pulmonary embolism, the study found. While no increased risk of bleeding was found in those with mild COVID, there was a noticeable increase in patients with more severe infection.

The study was led by Anne-Marie Fors Connolly of the department of clinical microbiology at Umeå University in Sweden.

Frederick Ho of the Institute of Health and Wellbeing at the University of Glasgow in Scotland and his colleagues wrote an editorial that accompanied the findings.

Even though many countries are removing pandemic restrictions and shifting their focus to living with COVID-19, this study "reminds us of the need to remain vigilant to the complications associated with even mild SARS-CoV-2 infection, including thromboembolism," Ho's team wrote.

More information

There's more on COVID-19 and the blood at the U.S. National Heart, Lung, and Blood Institute.

SOURCE: BMJ, news release, April 6, 2022