Blood Flow and Veins

Coronavirus Causing Blood Clots

Last updated on November 19th, 2022 at 11:56 am

This article will summarize coronavirus linked blood clots and what it can do to you. You will learn about the symptoms, treatments, and how to prevent coronavirus causing blood clots.

Doctors around the world are trying to make sense of the wide range of effects that COVID-19, the disease caused by the novel coronavirus, can have on the body.

Most people associate the infection with respiratory symptoms, fever, cough, fatigue. But many patients who contract the virus experience neurological symptoms such as headache and dizziness, as well as heart issues, kidney complications, and, most recently, blood clotting (also called coagulation).

Coronavirus Causing Blood Clots – What You Need to Know

As well as causing severe respiratory problems, there is mounting evidence COVID-19 causes abnormalities in blood clotting. Patients with severe COVID-19 infection appear to be at greater risk of developing blood clots in the veins and arteries. Blood clots can occur deep in the veins of the leg (deep vein thrombosis) and can move to the lungs, causing a pulmonary embolism, which restricts blood flow and oxygen and can be fatal.

Blood clots in arteries can cause heart attacks when they block the blood supply to the heart, or strokes when they block oxygen supply to the brain. So what is going on in the bodies of people with coronavirus? And what are clinicians doing to treat or prevent this complication?

Low levels of oxygen

COVID-19 also appears to be associated with blood clots in the tiny blood vessels that are important for transferring oxygen in organs. Autopsy reports have shown elements of SARS-CoV-2, the virus causing COVID-19, in cells lining these small blood vessels in the lungs, kidney, and gut.

This may cause tiny blood clots in these small blood vessels that disturb normal blood flow and the ability of the blood to deliver oxygen to these organs. Importantly, these small blood clots could reduce normal lung function. If these small blood clots reach the lungs, it may prevent oxygen from getting into the blood as efficiently as normal. This may explain why patients with severe COVID-19 can have very low oxygen levels.

What do these coronaviruses linked blood clots do?

The clots have taken various shapes and forms in different patients. In milder cases, the clots which appear to be scattered throughout the body have been linked to rashes or swollen, red toes (recently deemed “COVID toes”). In more severe cases, the clots can block an artery and cause a pulmonary embolism or trigger a heart attack or stroke.

It’s unclear why so many patients admitted to the hospital with COVID-19 are developing clots. One study found that nearly a third of COVID-19 patients in intensive care had clotting.

The Clots are Often Tiny and Everywhere

When we typically talk about blood clots, we’re looking at one or two major clots that block off blood supply to the brain and heart (and therefore cause a stroke or heart attack). But with COVID-19, rather than one or two big clots, doctors are seeing tons of tiny clots forming all over the place in the lungs, mostly, but also in the legs, feet, and just below the surface of the skin (which may cause those COVID toes).

“You may think itsy-bitsy clots would be less harmful. But they may actually be a sign that a much more severe illness is brewing. Just because the clots are smaller and evenly distributed doesn’t mean that they can’t be life-threatening,” Matthew Heinz, a hospitalist and internist at the Tucson Medical Center.

“They can show that clotting cascade those clotting derangements have now begun, and they could form everywhere, and you could end up with little clots forming in the coronary arteries that would give you a heart attack. And in the small arteries of the brain, that could give you focal strokes,” Heinz said.

This is probably why we’re seeing coronavirus patients in their 30s and 40s who don’t have any other risk factors to develop strokes, Heinz added.

The Clots Could be Because of Inflammation or Blood Vessel Injury

Though data is limited, one prominent theory behind the clots is that they’re triggered by the wave of inflammation COVID-19 triggers.

You may have heard about the “cytokine storm” that some people with COVID-19 experience. This occurs when the immune system overreacts, and instead of fighting the virus, cells kill themselves.

“This is a profound, body-wide systemic inflammatory response because of the viral infection,” Heinz said. “In highly infected, inflamed states, you can become hypercoagulable, or more likely to form clots everywhere.”

Another explanation for the clots is that the coronavirus directly injures the blood vessels. If this is the case, it would mean that the coronavirus is infecting the cells in our blood vessels. The body then views that infection as an injury and causes the blood to clot around it.

Patients Stuck on Bedrest Have More Risk Factors

There’s also the problem with very sick people being on bed rest, which allows blood to pool in the body. Asher Marks, a Yale Medicine pediatric hematologist, said COVID-19 patients in the ICU may experience stasis, or a “lack of flow of blood, often seen when patients are stuck in bed.”

Plus, most people who get extremely sick from COVID-19 already have risk factors that increase their chances of clotting. Many of these conditions, such as high blood pressure, diabetes, and heart disease, already put wear and tear on the blood vessels, and COVID-19 may make things worse.

“While we don’t know all the details who are at greater risk for developing blood clots, we see this most often in those patients who are critically ill because of COVID-19. Basically, there’s a lot going on in the body: the inflammation, injury of the blood vessels and bed rest that, together, cause a perfect storm for clots, ” Heinz said.

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Why does COVID-19 cause blood clotting?

One theory is that the increased rate of blood clots in COVID-19 is simply a reflection of being unwell and immobile. However, the current data suggest the risk of blood clots is significantly greater in patients with COVID-19 than what is usually seen in patients admitted to hospitals and ICUs.

Another potential explanation is that the virus is directly affecting the cells lining our blood vessels. When the body fights an infection, the immune system becomes activated to kill the invader, and research shows an activated immune system can cause blood clots.

In severe COVID-19, the immune system appears to go into overdrive. This could lead to the unchecked activation of cells that typically stop blood clotting.

Another possibility is that the virus triggers blood clotting to provide it with a survival advantage. The SARS virus, another member of the coronavirus family, can be further “activated” by a blood-clotting protein, enabling the virus to more efficiently invade cells.

However, whether this is the case with COVID-19 remains to be investigated.

Who has the greater risk of coronavirus linked stroke?

Patients who present to hospital with COVID-19 are also more likely to have a stroke when compared with the general population. Typically, the chance of having a stroke is associated with increasing age, as well as other risk factors such as high blood pressure, elevated cholesterol levels, or smoking.

However, higher rates of strokes in patients with COVID-19 is unusual because it also seems to happen in people under 50 years of age, with no other risk factors for stroke.

Treating and diagnosing coronavirus linked clots is difficult

When patients are admitted to hospital for coronavirus or any other condition that leaves them bed-bound, it is common practice to administer low-dose blood thinners to prevent the development of blood clots. However, given that patients with COVID-19 seem to be at a higher risk of developing blood clots, it’s currently being debated whether higher doses of blood thinners are required to prevent these clotting complications. Trials are underway to answer this important question.

Diagnosing these blood clots in patients with COVID-19 can also be challenging. First, the symptoms of a worsening lung infection associated with the virus can be indistinguishable from the symptoms of a pulmonary embolism. Another challenge in COVID-19 is that the virus can affect laboratory tests, which may also diagnose venous blood clots.

A good example of this is a test called D-dimer, which is a measure of clotting in the body. Normally, this test would be higher in almost everyone with new venous blood clots. However, people with severe COVID-19 infection can also have an elevated D-dimer simply because of the severe infection. In some patients, this means that the test is no longer helpful in diagnosing blood clots.


What we know for sure is that blood-clotting complications are rapidly emerging as a significant threat from COVID-19. In this area, we still have much to learn about the virus, how it affects blood clotting, and the best options for the prevention and treatment of these blood clots.

Understanding what causes the blood clots will probably answer some of the key questions about COVID-19, such as why underlying heart issues are more of a risk factor than lung problems or why so many infected patients seem to improve, then suddenly go into cardiac arrest or organ failure. This will give us the clues we need to better treat the infection and help more people in the ICU recover.

A clearer picture is coming together, but researchers agree they need more data to connect the dots and determine how and why the coronavirus causes major clotting problems.

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Sources And Original Content Published: HUFFPOST and The Conversation

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