Emerging evidence indicates that COVID-19, which is the disease that SARS-CoV-2 causes, leads to blood clots in an estimated 30% of critically ill patients.

A blood clot, or a thrombus, increases the risk of complications and death among those who have COVID-19. This disease causes blood clots in 20–30% of critically ill patients.

This article will look at the link between the novel coronavirus and blood clots and discuss some potential treatments and methods of prevention.

a woman sat on a bench and coughing into her arm because she has both coronavirus and bloodclotsShare on Pinterest
A person with a blood clot may experience a cough and sharp chest pain.

Blood clotting is one of the body’s natural responses to injury. It occurs when a volume of blood changes to a semi-solid state in order to prevent excessive blood loss. Several chemical reactions in the body facilitate this change.

Clots that form inside a deep vein, however, can be extremely dangerous. These clots may not dissolve on their own, and they can stop blood flow. This can be fatal.

In some situations, a clot can break off and travel to another part of the body. This thrombus becomes known as an embolus.

If the embolus reaches the brain, heart, or lungs, it can result in a life threatening condition, such as a heart attack or stroke.

The symptoms of a blood clot include:

According to a Nature article, researchers are not sure why COVID-19 causes blood clots.

One theory is that the clotting occurs when the novel coronavirus attacks the endothelial cells that line the blood vessels. The virus does this by binding to the ACE2 receptors, which are present in the endothelial cell membrane.

Once the virus binds to these receptors, the blood vessels start releasing proteins that trigger blood clotting.

Another theory is that COVID-19 causes the body’s immune system to trigger a hyperactive inflammatory response. This inflammation may then trigger clotting.

Other factors may also play a role in blood clotting in people with COVID-19. For example, many people who require hospital care due to the disease also have other risk factors for blood clots. These include:

Other viruses, including swine flu (H1N1) and SARS, also increase the risk of blood clots.

Blood clots in people with COVID-19 tend to differ from those present in people without the disease who have strokes or clots in the lungs.

According to a paper in the British Journal of Haemotology, in people with COVID-19, the clots appear to form within the lungs. Typically, however, clots tend to form in other areas of the body before breaking off and traveling to the lungs.

Also, in those with COVID-19, the clots seem to form in the tiny vessels of the lungs, rather than the major vessels, as is the case in typical strokes.

One small autopsy study in the Annals of Internal Medicine examined 11 deceased COVID-19 patients. The researchers report that all of them had evidence of varying degrees of blood clots. None of these people received a diagnosis of blood clots while they were alive.

The researchers hypothesize that the blood clotting was the cause of death, despite the fact that 10 of the 11 the patients received anticoagulation, or anti-clotting, treatment.

A 2020 study in the New England Journal of Medicine compared the lungs of seven people who died from COVID-19 with the lungs of seven people who died from H1N1.

The researchers found that the lungs of those with COVID-19 had nine times the number of clots than the lungs of those with H1N1.

Learn more about blood clots in the lungs here.

Excessive blood clotting in people with COVID-19 may be responsible for several complications arising from the disease.

Research indicates that people with COVID-19 who have a higher rate of blood clotting activity tend to have a significantly worse outcome than others. They are also more likely to require treatment in the intensive care unit.

Some potential complications of blood clots include:


When a blood clot blocks an artery in or around the brain, it can trigger a stroke.

A preliminary observational study indicates that younger COVID-19 patients with no other risk factors for stroke have an increased risk, even if they do not have symptoms of the disease.

The researchers also report seeing strokes in people in their 30s, 40s, and 50s that tend to be typical of people in their 70s and 80s.

Heart damage

A blood clot in the arteries can cause a heart attack or other cardiac issues. According to a study of 187 patients with COVID-19 at a hospital in Wuhan, China, 27.8% of the patients developed damage to the heart.

Pulmonary embolism

Blood clots that travel to the lungs cause pulmonary embolisms, which can be fatal. Prompt treatment significantly reduces the risk of death.

Deep vein thrombosis

Deep vein thrombosis (DVT) occurs when a blood clot forms in a vein deep in the body, such as in a leg or an arm.

In the autopsy study, DVT was present in almost 60% of those who died from COVID-19. Without treatment, DVT can lead to pulmonary embolism, amputation, or death.

Kidney damage

Some people with severe COVID-19 develop kidney damage, even if they did not have kidney issues before contracting SARS-CoV-2. In some cases, the damage is so severe that people require dialysis treatment.

Blood clots may play a role in kidney damage because they can clog the tiny blood vessels in the kidneys, reducing their ability to function.

Some factors that increase the risk of developing blood clots include:

  • being older
  • carrying excess weight
  • having hypertension
  • having diabetes
  • having heart failure
  • taking medications that increase the risk of blood clotting
  • having periods of inactivity, such as prolonged bed rest
  • undergoing surgery
  • smoking
  • having a personal or family history of DVT or pulmonary embolism
  • having a blood clotting disorder

Doctors may treat or prevent blood clots by prescribing blood-thinning medications. Many doctors will start this treatment during a person’s hospital stay and continue it for 2 weeks after discharge to reduce the risk of blood clots.

However, taking blood thinners also increases the risk of bleeding, which may make them unsuitable for high risk patients. There are some reports that people on mechanical ventilation with COVID-19 who took blood thinners had a lower mortality than those who did not take the medication.

Researchers are also testing new therapies to help treat and prevent blood clots.

Some scientists are comparing standard doses of blood thinners with higher doses in critically ill people. Others are testing the effects of more potent medications, such as tissue plasminogen activator.

According to the World Health Organization (WHO), most people who develop COVID-19 will experience mild-to-moderate respiratory symptoms. They are also unlikely to require any special treatment.

Those with additional risk factors are more likely to develop severe illness, including blood clots.

The best way to prevent infection with the novel coronavirus is to practice good hand hygiene and physical distancing.

People at increased risk of blood clots should speak to their doctor. In some cases, the doctor may recommend using a blood-thinning medication. However, these medications are not suitable for everyone.

Some other ways to reduce the risk of blood clots include:

  • staying active as much as possible
  • wearing special stockings to improve blood flow
  • drinking plenty of water to prevent dehydration
  • losing weight, if necessary
  • avoiding alcohol and tobacco use

Experts do not fully understand why the novel coronavirus causes blood clots in some people. These clots typically develop in the lungs, but they may also develop in other areas of the body.

Blood clots increase the risk of complications, including stroke, heart problems, and death.

People who have concerns about their risk of blood clots should speak to their doctor. However, it is important to remember that most people who develop COVID-19 will develop mild-to-moderate symptoms and recover without complications.