Risk of blood clots rises in Covid-19 patients, Swedish study finds

Patients with Covid-19 face an increased risk of serious blood clots up to six months after being infected, according to new research.

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There is an increased risk of pulmonary embolism – a blood clot in the lung – up to six months after infection, the study by Swedish researchers indicates.

For deep vein thrombosis – a blood clot in the leg – there is an increased risk for up to three months and for bleeding events up to two months, they found.

From the records of more than one million people with Covid-19 and four million who were not infected, the researchers identified 401 patients who had the disease and suffered a deep vein thrombosis, and 267 cases in the control group.

There were 1,761 pulmonary embolisms in the Covid-19 group and 171 in the control group, and 1,002 bleeding events in the Covid-19 group against 1,292 in the control group.

Risk of bleeding

The researchers found a fivefold increase in the risk of deep vein thrombosis, a 33-fold increase in the risk of pulmonary embolism, and an almost twofold increase in the risk of bleeding in the 30 days after infection.

Even among mild, non-hospitalized Covid-19 patients, the researchers found an increased risk of deep vein thrombosis and pulmonary embolism. No increased risk of bleeding was found in mild cases, but a noticeable increase was observed in more severe cases.

The study is observational, so the researchers cannot establish cause. They also note limitations such as possible underdiagnosis of clotting, limited testing for Covid and the non-availability of information on vaccination.

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