Several research teams writing in the journal Radiology suggest that blood clots play a significant role in why some people become seriously sick with COVID-19.

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Blood clots may lead to serious complications in some people with severe COVID-19.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

The death toll from COVID-19 continues to rise daily. But how SARS-CoV-2, the new coronavirus that causes the disease, actually causes death remains poorly understood.

Clinical reports show that people with severe COVID-19 develop pneumonia, acute respiratory distress syndrome, and multiple organ failure.

Age and underlying medical conditions are factors that increase a person’s risk of severe disease.

In a collection of articles published in the journal Radiology, experts now highlight that a significant proportion of those with severe COVID-19 show signs of blood clots, which can lead to life-threatening complications.

Blood clotting is a natural mechanism in response to an injury. However, when a blot clot forms within a blood vessel, it can restrict blood flow. Known as a thrombus, it can lead to severe medical emergencies.

If a thrombus breaks free and travels to another part of the body, doctors call it an embolus. If an embolus reaches the lungs, brain, or heart, the ensuing embolism can become life-threatening.

But why would thrombi and emboli be an issue in COVID-19? The SARS-CoV-2 virus can infect cells in the lung. In severe cases, this leads to inflammation in the lungs and shortness of breath.

Yet, how breathlessness or impaired pulmonary ventilation progresses to death is not entirely clear.

“Worldwide, COVID-19 is being treated as a primary pulmonary disease,” explains Professor Edwin van Beek from Queens Medical Research Institute at the University of Edinburgh in the United Kingdom. “From the analysis of all available current medical, laboratory, and imaging data on COVID-19, it became clear that symptoms and diagnostic tests could not be explained by impaired pulmonary ventilation alone.”

Prof van Beek is the senior author of one of the papers in Radiology. Along with a team of experts, he reviewed whether blood clots might play a role in COVID-19.

Viral infections can activate the blood clotting pathway. Experts believe that this process evolved as a mechanism to limit the spread of a viral infection.

To assess blood clotting in a person, healthcare professionals often measure the amount of a protein complex called D-dimer they have in their blood. D-dimer remains in the blood after an enzyme called plasmin degrades the blood clot in a process called fibrinolysis.

High D-dimer levels in the blood are an indication of thrombosis and embolism.

Reviewing the evidence to date, Prof. van Beek and his colleagues write: “There is a strong association between D-dimer levels, disease progression, and chest CT features suggesting venous thrombosis.”

Radiology has also published a research letter written by a team from Centre Hospitalier Universitaire de Besancon in France. The group reports that 23 out of 100 patients in the hospital with severe COVID-19 had signs of pulmonary embolism, which is a blood clot that has traveled to the lung.

These patients were more likely to be in the critical care unit and require mechanical ventilation than those without pulmonary embolism.

Another research team from Hôpitaux Universitaires de Strasbourg in France echoed the findings. In their research letter, also published in Radiology, the team reports that 30% of 106 patients in the hospital with severe COVID-19 showed signs of blood clots in their lungs.

According to the authors, “This rate of [pulmonary embolus] is higher than usually encountered in critically ill patients without COVID-19 infection (1.3%) or in emergency department patients (3–10%).”

The Strasbourg team also found that these people also had higher levels of D-dimer in their blood than those without pulmonary embolus.

In his paper, Prof. van Beek explains that there is already evidence of a link between high levels of D-dimers and poor outcomes for patients with COVID-19.

As researchers begin to understand more about how and why COVID-19 is deadly for some people, this knowledge will help identify the best treatment options.

In light of their analysis, Prof. van Beek and his colleagues recommend measuring D-dimer levels, monitoring for signs of embolism or thrombosis, and early initiation of anticoagulation therapies to avoid blood clots.

“COVID-19 is more than a lung infection. It affects the vasculature of the lungs and other organs. It has a high thrombosis risk with acute life-threatening events that require adequate treatment with anticoagulants based on laboratory monitoring with appropriate imaging tests as required.”

– Prof. Edwin van Beek

One of the team’s recommendations is to give a low dose of heparin, which prevents clot formation, to all patients admitted to the hospital with suspected or confirmed COVID-19.

Other scientists have recently suggested using tissue plasminogen activator (tPA), which helps to dissolve blood clots, to treat people with severe COVID-19.

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