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COVID-19 and Blood Clotting

Medically reviewed by Susan Kerrigan, MD and Marianne Madsen

Doctors have been noticing an increased prevalence of blood clots in hospitalized COVID-19 patients. Up until recently, it was thought that the 2019-2020 coronavirus was primarily a respiratory disease, affecting mostly the lungs. But now, scientists think that the virus may attack blood vessels as well.


The dangers of blood clots


Blood clotting is particularly dangerous because clots can travel from the bloodstream to the lungs or brain, causing serious complications such as stroke. Blood clots can happen at any age but risk factors such as smoking, surgery, and cancer can increase your likelihood for developing one. Almost 100,000 Americans die every year from blood clotting.

Blood clots found in deceased COVID-19 patients


A review of seven COVID-19 patient autopsies found that blood clots were present throughout the body in those who succumbed to the disease. The pathologists who performed the review weren’t sure what caused the blood clotting, which was detected mostly in the heart and lungs. All deceased patients, however, had multiple comorbidities, and all but two were obese.

Theories for the link


Scientists have no concrete answers for the association between COVID-19 and blood clotting, but some theories aim to explain the link. One theory states that in some, the body’s immune response to the virus causes inflammation of the blood vessels, which in turn leads to blood clots.


Another more complicated theory involves endothelial cells, which are found in the inner lining of blood vessels. Endothelial cells are covered in proteins called angiotensin-converting enzyme 2 (ACE2) receptors. Scientists say that the coronavirus attaches itself to the ACE2 receptors once inside the body, and through this mechanism it attacks cells. This way, the virus gets into the blood vessels and causes blood clotting, according to Dr. Gary Gibbons, Director of the NIH’s Heart, Lung, and Blood Institute.


“We’re still in the early days of learning about this virus… In fact, clots have been reported at the capillary level, and that’s fairly unusual. It’s suggestive that an interaction is taking place between the platelets and the endothelial surface,” said Gibbons. “It’s incredible the tricks this virus has learned by binding onto one of these molecules in the endothelial lining.”

Who is at risk for this new COVID-19 symptom?


Dr. Gibbons emphasizes that older adults are “among the most vulnerable” for getting blood clots as a result of the coronavirus disease. “They have a lot of the risks for the formation of these blood clots,” he said. But he also noted that some younger adults have also reportedly developed blood clotting from the virus. It seems that the people most at risk, though, are older adults who have preexisting conditions that already increase their risk for blood clotting.


As the coronavirus is still being researched worldwide, we continue to discover new potential symptoms in the infected. With any luck, a treatment will be available that reduces blood clotting as well as the other side effects of this virus.

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