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Increased risk of blood clots long after COVID-19

Several months after COVID-19, one is still at an increased risk of blood clot and bleeding, shows research from Umeå University.

The researchers analyzed all COVID-19 cases in Sweden from the start of the pandemic until May last year.

“The results underline the importance of people getting vaccinated against COVID-19 but also of healthcare providers identifying individuals with COVID-19 who are at increased risk of blood clots so that blood thinners can be used,” says Ioannis Katsoularis, doctoral student at Umeå University and cardiologist at University Hospital of Umeå.

The risk of developing pulmonary embolism stayed increased up to six months after COVID-19

In the study, the researchers found that the risk of developing deep vein thrombosis (i.e. blood clots in the deep blood vessels), stayed elevated for up to three months after COVID-19. During the first month, this risk was five times higher than for people without COVID-19. Among hospitalized COVID-19 patients, the risk of bleeding was also two-fold increased.

When a blood clot lodges in the lung, a potentially fatal condition emerges, called pulmonary embolism. The researchers observed that the risk of developing pulmonary embolism stayed increased up to six months after COVID-19. In particular, the risk of pulmonary embolism during the first month was 32 times higher than in individuals without COVID-19. It was also observed that among those who were on treatment with blood thinners since before COVID-19, the risk of pulmonary embolism was 70% lower, suggesting a protective effect.

The risk of blood clots and bleeding increased with the severity of COVID-19, and was highest in patients who required intensive care.

The study was based on data from national registers from the Swedish National Public Health Agency and the Swedish National Board of Health and Welfare. All individuals in Sweden with a positive SARS-COV-2 test from the start of the pandemic until May 2021 were included in the study. The researchers calculated the incidence of blood clots and bleeding after SARS-CoV-2 infection and compared it to the incidence of these conditions in individuals without the infection. The risk of these complications was calculated using two different methods; a matched cohort study and a self-controlled case series study.

Source: Ola Nilsson/Umeå University

Photo: iStock