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Elevated Danger of Severe Blood Clots As much as Six Months After COVID-19

Blood Clot Scanning Electron Micrograph

Scanning Electron Micrograph (SEM) picture of a blood clot.

Analysis uncovered an elevated threat of pulmonary embolism (a blood clot within the lung) as much as six months after covid-19 an infection, deep vein thrombosis (a blood clot within the leg) as much as three months, and a bleeding occasion as much as two months. The research from Sweden was printed by The BMJ.

In accordance with the findings, there’s additionally a better threat of occasions in sufferers with underlying situations (comorbidities), sufferers with extra extreme covid-19, and through the first pandemic wave in contrast with the second and third waves.

These outcomes help measures to stop thrombotic occasions (thromboprophylaxis), particularly for high-risk sufferers, and strengthen the significance of vaccination in opposition to covid-19, in line with the researchers.

It’s already properly established that covid-19 will increase the danger of significant blood clots (often called venous thromboembolism or VTE), however much less proof exists on the size of time this threat is elevated, if threat modified through the numerous pandemic waves, and whether or not covid-19 additionally will increase the danger of main bleeding.

To deal with these uncertainties, scientists got down to measure the danger of deep vein thrombosis, pulmonary embolism, and bleeding after covid-19.

Utilizing nationwide registries in Sweden, they recognized multiple million individuals with confirmed SARS-CoV-2 infection (the virus responsible for covid-19) between February 1, 2020 and, May 25, 2021, matched by age, sex, and county of residence to more than four million people who had not had a positive SARS-CoV-2 test result.

They then performed two analyses: in the first, they calculated the rates of deep vein thrombosis, pulmonary embolism, and bleeding in covid-19 individuals during a control period (before and long after covid-19 diagnosis) and compared it to the rates in different time intervals after covid-19 diagnosis (days 1-7, 8-14, 15-30, 31-60, 61-90, and 91-180).

In the second analysis, they calculated the rates of deep vein thrombosis, pulmonary embolism, and bleeding during the period 1-30 days after covid-19 diagnosis in the covid-19 group and compared them to the corresponding rates in the control group.

The results show that compared with the control period, risks were significantly increased 90 days after covid-19 for deep vein thrombosis, 180 days for pulmonary embolism, and 60 days for bleeding.

After taking into account a range of potentially influential factors, 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.

In absolute terms, this means that a first deep vein thrombosis occurred in 401 patients with covid-19 (absolute risk 0.04%) and 267 control patients (absolute risk 0.01%). A first pulmonary embolism event occurred in 1,761 patients with covid-19 (absolute risk 0.17%) and 171 control patients (absolute risk 0.004%), and a first bleeding event occurred in 1,002 patients with covid-19 (absolute risk 0.10%) and 1,292 control patients (absolute risk 0.04%).

Risks were highest in patients with more severe covid-19 and during the first pandemic wave compared with the second and third waves, which the researchers say could be explained by improvements in treatment and vaccine coverage in older patients after the first wave.

Even among mild, non-hospitalized covid-19 patients, the researchers found increased risks 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.

This is an observational study, so the researchers cannot establish cause, and they acknowledge several limitations which might have affected their findings. For example, VTE may have been underdiagnosed in patients with covid-19, testing for covid-19 was limited, especially during the first pandemic wave, and information on vaccination was not available.

However, results were largely consistent after further analyses, and are in line with similar studies on the association between covid-19 and thromboembolic events, suggesting that they withstand scrutiny.

As such, the researchers say their findings suggest that covid-19 is an independent risk factor for deep vein thrombosis, pulmonary embolism, and bleeding, and that the risk of these outcomes is increased for three, six, and two months after covid-19, respectively.

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

In a linked editorial, researchers at the University of Glasgow point out that despite the potential for new variants of concern, most governments are removing restrictions and shifting their focus to determining how best to “live with covid.”

However, they say this study “reminds us of the need to remain vigilant to the complications associated with even mild SARS-CoV-2 infection, including thromboembolism.”

Reference: “Risks of deep vein thrombosis, pulmonary embolism, and bleeding after covid-19: nationwide self-controlled cases series and matched cohort study” by Ioannis Katsoularis, Osvaldo Fonseca-Rodríguez, Paddy Farrington, Hanna Jerndal, Erling Häggström Lundevaller, Malin Sund, Krister Lindmark and Anne-Marie Fors Connolly, 6 April 2022, The BMJ.
DOI: 10.1136/bmj-2021-069590

Funding: Region Västerbotten Agreement for Medical Education and Research funding, Umeå University, the Laboratory for Molecular Infection Medicine Sweden, Stroke Research in Northern Sweden, the Swedish Kidney Foundation, the Scandinavian Research Foundation for venous diseases, the Heart Foundation in Northern Sweden, Arnerska Research Foundation, and Kempes Foundation



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