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COVID-19 is an illness that’s caused by the new coronavirus, SARS-CoV-2. Many symptoms of COVID-19, such as cough and shortness of breath, affect your respiratory system.

However, the virus can also have other effects on your body. For instance, in some cases it can cause gastrointestinal symptoms, loss of smell or taste, or even a toe rash.

Another possible side effect of COVID-19 is that it can lead to blood clots in some people.

In this article, we’ll take a closer look at how COVID-19 can contribute to the formation of blood clots, who’s at higher risk, and the treatment options.

Normally, blood clots help stop bleeding when you’re injured.

When a blood vessel is injured, it produces proteins that attract platelets and other clotting factors. These clump together to form a clot that plugs the injury and allows it to heal.

However, sometimes blood clots form in the absence of an injury. This is potentially dangerous because the clot can restrict the flow of blood within your blood vessels, leading to complications like stroke or heart attack.

Blood clots with COVID-19 have most often been seen in people who’ve been hospitalized with the disease.

A study of 184 people in the ICU for severe COVID-19 found that 31 percent of these individuals experienced complications related to blood clots.

It’s still unknown how common blood clots are in individuals who have a mild case of COVID-19.

COVID-19 complications from blood clots can happen across all ages. A small study looked at 14 people with COVID-19 who had experienced a stroke due to a blood clot.

The study found that 42 percent of participants were under age 55 and had no existing risk factors for stroke.

It’s still unclear why blood clots develop in people with COVID-19. However, a recent study, published in the journal The Lancet Haematology, helps shed some light on this topic.

The study involved 68 people hospitalized with COVID-19. Of these people, 48 were in the ICU and 20 were not. Their blood was analyzed for various markers associated with clotting.

The markers in question are involved with the activation of the cells lining your blood vessels (endothelial cells) and platelets. Both endothelial cells and platelets are important for starting the clotting process.

The study found that the people in the ICU had higher levels of these clotting markers than those who weren’t in the ICU.

The exact cause of the increase in clotting markers is uncertain, but it could be due to one (or a combination) of the mechanisms below:

  • Endothelial cells express ACE2 protein, which the new coronavirus uses to enter cells. Because of this, the virus could directly invade and damage endothelial cells, triggering your body’s clotting mechanism.
  • If endothelial cells aren’t being directly infected, damage to the tissues around them due to viral infection or your immune response could cause increased clotting.
  • An increase in inflammatory molecules that your immune system produces in response to viral infection could activate clotting.

Another study that was published in the journal Blood supports some of the findings above.

In this study, the platelets of people hospitalized with COVID-19 were found to be hyperactive, having increased activation and aggregation (clumping).


Although the exact mechanism is unclear, COVID-19 appears to cause increased activation of cells that are important in initiating the clotting process. This may lead to an increased risk of blood clots.

You may be at higher risk for blood clots from COVID-19 if you:

  • Are hospitalized. Most cases of blood clots in people with COVID-19 have been reported in individuals who’ve been hospitalized.
  • Have high levels of certain markers. A study of more than 300 people hospitalized with COVID-19 found that high D-dimer levels were a strong predictor of death. Other clotting and inflammatory markers have also been associated with clotting or poor outcome.
  • Have other conditions that put you at risk for clotting. Some examples include heart disease, diabetes, and obesity.

Having a blood clot can lead to some potentially serious complications, such as:

  • Stroke. A blood clot can block blood vessels in your brain, interrupting blood flow and leading to a stroke. If a clot temporarily reduces blood flow, you can have a transient ischemic attack (TIA), or ministroke.
  • Pulmonary embolism. A pulmonary embolism is when a blood clot travels to your lungs and blocks the flow of blood. This can decrease oxygen levels and damage lung tissue.
  • Heart attack. A heart attack happens when blood flow to your heart tissue is cut off. Blood clots are a potential cause of heart attacks.

It’s also possible that a blood clot could restrict blood flow in other parts of your body, causing potentially serious damage. Some examples of other areas that a blood clot may affect include your:

COVID-19 and capillaries

Capillaries are the smallest blood vessels in your body. They can be so narrow that red blood cells must pass through them in a single-file line.

Clots due to COVID-19 can also affect capillaries. In fact, it’s possible that the presence of tiny clots in capillaries could contribute to the condition known as “COVID toes.”

These tiny clots can be dangerous in people with COVID-19 pneumonia, where inflammation and fluid buildup already make it difficult to breathe.

A clot in the capillaries inside the tiny air sacs of your lungs can restrict blow flow, further lowering oxygen levels.

People who have blood clots are often treated with a medication called a blood thinner, which reduces clotting in your body. Blood thinners can help prevent existing clots from getting bigger and keep new clots from forming.

One study examined the effects of blood thinners in people who were hospitalized with COVID-19. It found that people who were treated with blood thinners in the hospital had a more positive outcome than those who were not.

It’s important to note that this study was only observational and wasn’t a clinical trial.

Going forward, clinical trials will need to be performed to determine the safety, effectiveness, and proper dosage of blood thinners to treat COVID-19-related blood clots.

You can reduce your risk for blood clots in general by doing the following:

  • Stay active. A sedentary lifestyle can increase your blood clot risk, so make sure to get regular exercise. If you need to sit for a long time — like with working or traveling — try to take regular breaks so you can get up and move around.
  • Lose weight if you’re overweight. Shedding excess weight can help lower your risk for developing blood clots.
  • Don’t smoke. Smoking can damage the lining of your blood vessels and cause clots to form.
  • Know the side effects of medications. Some types of medications, including birth control pills, hormone replacement therapy, and certain cancer drugs, may increase your risk for blood clots. Work with your doctor to make sure these are properly managed to minimize the risk of blood clots.

The best way to help prevent COVID-19-related blood clots is by taking steps to avoid contracting the new coronavirus. The most effective way to avoid this highly contagious virus is to:

If you come down with COVID-19 and are concerned about your blood clot risk, don’t hesitate to speak with your doctor.

If you’re at increased risk for blood clots, it’s possible that your doctor may prescribe an oral blood thinner medication.

COVID-19 can potentially cause blood clots. So far, blood clots have mostly been seen in people who are hospitalized with severe COVID-19 symptoms.

It’s unclear exactly how COVID-19 leads to blood clots. However, the infection has been found to activate cells that are involved in the clotting process.

Blood clots due to COVID-19 can lead to complications like stroke and heart attack. These can occur across all age groups and in otherwise healthy people.

If you become ill with COVID-19 and are concerned about your blood clot risk, be sure to talk with your doctor.