May 31, 2020

Should You Be Worried About Blood Clots With COVID-19?

Your coronavirus blood clot questions, answered

blood clot formation

Experts are still learning exactly how COVID-19 affects the body. One worrisome symptom that has emerged is blood clots.


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“We’re seeing a higher rate of blood clots in patients hospitalized with COVID-19,” says pulmonologist Wayne Tsuang, MD. “But it’s not clear yet how common clots are in people with mild symptoms who are at home.”

Blood clots are associated with serious complications, such as stroke. Scientists are scrambling to learn more about why the clots are occurring in coronavirus patients and who is most vulnerable. Here’s what we know so far.

Why are blood clots dangerous?

A blood clot is a clump of blood. When blood clots, it changes from a liquid state to a thicker, gel-like state.

Clotting is your body’s natural way to stop bleeding. But when clots break free and travel through the bloodstream, they can block blood flow to essential organs such as the lungs (causing a pulmonary embolism) or brain (causing a stroke). “If the clots block a blood vessel, you can lose the blood supply to that organ,” Dr. Tsuang explains.

What’s the connection between COVID-19 and blood clots?

It’s not yet clear how or why COVID-19 is causing blood clots to form, Dr. Tsuang says. But there does seem to be a connection. One study in Amsterdam found that nearly one-third of people hospitalized with severe cases of COVID-19 had complications from blood clots.

Why are clots a risk for hospitalized patients?

Clots are most likely to arise in the blood vessels of the legs. People in the hospital are at higher risk, Dr. Tsuang explains.

“When you’re in the hospital, you’re not up and moving around, so blood moves more slowly through the legs. That makes clots more likely to form.”

How do doctors prevent clots in hospitalized patients?

“Doctors use a checklist to estimate the risk that a hospitalized patient has for developing blood clots,” Dr. Tsuang says. “Depending on the risk, there are therapies we can use to prevent clots from forming.”

Blood-thinning medications lower the risk for clots. Yet they also increase the risk of bleeding, so they aren’t always an option for high-risk patients.

Another way to prevent clots is to use special “boots” that wrap tightly around the legs. “The boots inflate with air to massage the legs and push the blood through, lowering the risk that a patient will develop blood clots,” Dr. Tsuang explains.

Are clots a risk for people with mild cases of COVID-19?

There are reports that clots are forming in people with COVID-19 who are at home and mobile — not just those lying flat in a hospital bed. But it’s not clear yet how common they are.

“When people are in the hospital, we’re more likely to do tests to look for clots. So we know more about this symptom in people with severe cases,” Dr. Tsuang explains. “In less ill patients who are recovering at home, we just don’t know yet.”

How can I prevent blood clots if I have COVID-19?

If you have other conditions that put you at risk for clots, your doctor may consider using a blood thinner to reduce your risk, Dr. Tsuang says. But there can be serious risks from increased bleeding, so don’t start any blood-thinning medications without consulting your doctor first.


The best thing you can do to reduce the risk, he adds, is to stay mobile. “Move around as much as you can. If you’re resting in bed, try to stretch your legs to keep blood circulating,” he says.

What are the signs of blood clots?

Some patients with the coronavirus have developed a symptom called “COVID toes” — red, swollen toes that might be due to small clots in the blood vessels of the feet. But it’s not clear how common COVID toes are.

In the legs, swelling is the most common sign of a blood clot, Dr. Tsuang says. “If you have significant swelling in one leg, call your doctor right away.”

Is there anything else I should do to prevent blood clots?

There’s no reason to panic about clots, but it’s important to understand the risk, Dr. Tsuang says. If you’re being treated for COVID-19, start a conversation about blood clots with your medical providers.

“Ask your doctor about the best strategy,” he says. “The medical community is working toward finding the optimal strategy to prevent clots.”

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