Does Covid Increase The Chances Of Blood Clot?

Doctor with surgery procedure

Coronavirus infection is associated with a higher risk of blood clots for several reasons.


Have you ever noticed that it clots within seconds whenever the blood comes through a wound? Why and how does this occur? Clotting is a vital physiological process that prevents excessive blood loss in the case of an injury and helps maintain the blood flow in the vessels. But what if this clotting starts to occur inside your body? Various infections are associated with a higher risk of developing severe blood clots. The devastating COVID-19 pandemic is also among these diseases.

How blood clots?

It will clot immediately when your blood is exposed to air and a rough surface. Clotting is a complex event and involves a cascade of events and different molecules. A damaged blood vessel produces different chemicals that attract the platelets to the injury site. These platelets react with fibrinogen (a blood protein) and different clotting factors and form a clump of cells known as a blood clot.

Timely clotting in case of a wound helps stop bleeding and start healing. If the clotting cascade is disturbed for one or the other reason, bleeding may not occur, and a minor injury could bleed you to death. Clotting also helps your blood to stay in the vessels. In case of clotting failure, e.g., in platelet deficiency, you may die due to internal bleeding (haemorrhage). If the controls over the process fail, your blood will start clotting inside the veins and arteries, thus impeding them and stopping blood flow.

Can you afford both of these issues?

COVID-19 and blood clots

The devastating coronavirus pandemic entered the United Kingdom in February 2020. According to, more than 22 million people have been infected, with the total death toll exceeding 175,000. The death rate is particularly high in high-risk patients, e.g., in elderly people, those with chronic infections and cardiovascular diseases. 

If you are more interested in an overview of COVID-19, then read our comprehensive guide written by DR. Williams, which includes symptoms, causes and testing for COVID-19. 

Blood clots in the COVID pandemic have become a serious concern for the medical community. The issue was highlighted by a Swedish study that identified the coronavirus as an independent risk factor for clotting and found that COVID patients had a very high risk of developing blood clots in the lungs that could be very dangerous. The clotting problems could also lead to other issues, e.g., bleeding and deep vein thrombosis (DVT) (blood clots in the deep veins) after the COVID infection. The study found a 33 times more risk of lung clots, a five times more risk of DVT, and a two times more risk of bleeding in the month following the COVID infection.

Why do such clots occur? What would be the consequences of blood clotting? How can you reduce the risk of these clots? Let's summarize these issues in the coming lines. Stay on the page for answers.

Why do blood clots form in coronavirus infection?

But what is in the virus that causes increased clotting? For this, you should understand the clotting cascade. The clotting cascade is a sequence of complex events that occur under the influence of certain molecules called clotting factors or clotting markers.

A 2020 study published in the Journal of Clinical Medicine identified elevated levels of various clotting factors in the blood of COVID-19 patients. These markers are known to activate endothelial cells of blood vessels (the cells that line the inner wall of blood vessels) and platelets. Both of these cells have an important role in the clotting process.

Another study by Zhang and his colleagues in 2020 found that the levels of different clotting factors were significantly increased in critically ill COVID-19 patients compared to those with a milder infection. The increase in the ranks of clotting factors noted was;

  • D-Dimer 100%
  • Prothrombin time 73.7%
  • Fibrinogen 73.7%
  • Factor VIII 307%

But why these clotting factors are increased? The scientific investigations have identified the following factors.

  • Due to acute infection, the body releases a range of inflammatory chemicals due to the activation of the immune system. These chemicals interfere with the clotting factors and increase the chances of blood clots.
  • The integrity of the endothelial cell surface is very important for clotting. The coronavirus enters the blood through these cells, thus damaging them. The damage to these cells initiates the clotting mechanisms.
  • Damage to the cells around the endothelial cells due to the virus can also activate the clotting process.
  • Another study found that the platelets of hospitalised patients were more active. Thus, they are more prone to clumping together and forming clots.

What will be the Consequences of blood clotting

The increased risk of developing dangerous blood clots in COVID-19 is associated with severe clinical outcomes. The blood clots formed in the vessels supplying any organ can disrupt the blood supply to that area. The most common regions affected by COVID-related clots are the gastrointestinal tract, kidneys, and limbs. Besides this local area influence, the clots can increase the chances of some potentially dangerous complications, e.g.,

Heart attack


heart attack and blood clotting

Figure 3: Blood clots can increase the risk of a heart attack. Image courtesy:

Imagine that stray clots are lodged in your heart arteries? What will be the result? Not good. The blood supply to the heart will be cut off, and heart cells will start dying, a terrifying heart attack. You will end up in the ICU of a hospital and may not return alive.

Brain stroke

blood clot signs

Figure 4: Clots can lodge in the brain and cause brain stroke. Image courtesy:

Suppose similar clots lodge in your brain arteries. The result will be a brain stroke. Even a ministroke due to temporary blocking can kill you. A 2020 study in China involving 214 patients hospitalised for covid 19 found that 36.4% of the patients had neurological signs related to cerebral stroke due to coagulopathy.

Pulmonary embolism

Embolism means a process in which a clot formed in one space travels to another narrow area. If a lump develops in the limbs or other regions and travels to the lungs and lodges here, pulmonary embolism will be the outcome. What will happen? Your lung tissue will be damaged, respiratory efficiency reduced, and you will find difficulty in normal respiration.

A meta-study published in the European Journal of Internal medicine found that 14.7% of the patients admitted to the hospital's general ward or intensive care units (ICUs) had a severe pulmonary embolism. The study reviewed the data of 7178 patients with covid-19.

Note your oxygen saturation. Whenever it falls below 92%, it is a signal of concern.

Can a COVID vaccine cause clots?

It is often asked whether a vaccine can cause blood clots. It's common to give some blood thinner with some vaccines, e.g., AstraZeneca. But, according to experts, the clots can rise, and the risk of clotting events may increase after a vaccine, but these effects are temporary and recover within a short time after the vaccine. So, the vaccine is a worthy option to consider.

Moreover, the overall risk of clotting events is negligibly small. For example, a study by the Medicines and Healthcare products regulatory agency (MHRA) in the UK in 2021 found only 79 clotting events after the first dose of the vaccine. During the same period, more than 20 million vaccine doses were administered. The other vaccines, e.g., Moderna and Pfizer-BioNTech, are not associated with clotting issues.

So, the local authorities should extend the treatment and vaccine coverage to the people.

What to do if you experience clotting events?

Have you ever got COVID infection? The second and third waves infected a huge proportion of the population. If you have ever gone through it, you should remember the painful 'COVID toes'. These are the signs related to blood clots in peripheral capillaries due to COVID. Consult the pulmonologist if you are in the active infection phase or have recently recovered, or are going for vaccines (particularly AstraZeneca).

Decreasing oxygen saturation and worsening respiratory symptoms also suggest that you may have a pulmonary embolism. In any of these situations, consult your pulmonologist about the treatments. He may advise you;

Blood thinners

These Medicines will prevent clot formation, but they will also prevent smaller clots from going bigger. However, blood thinners are a topic of debate and require further clinical trials.

Lifestyle changes

Leaving the medicine-related issues to your physician, what can you do in this situation?

healthy lifestyle

Figure 5: Healthy lifestyle can help you enormously. Image courtesy:

The following lifestyle changes could help you to cope with the situation.

Consult the doctor if you are using other medications

If you are using contraceptives, hormonal therapies, and taking some anticancer drugs, tell immediately to your doctor. These medications are known to influence the Clotting process.

Stay active

Try to remain active and do some exercise regularly. If you have to sit for a prolonged period, e.g., during study or work, it is good to take breaks after regular periods.

Lose weight

Excessive weight can also increase the chances of blood clots.

Quit smoking

Smoking can damage the endothelial cells of blood vessels and increase the chances of clots. So, it is a good option to skip smoking.

Follow COVID-19 precautions

Stick to all infection control protocols, e.g.,

  • Use a face mask in public.
  • Practice physical distancing
  • Practice regular hand washing
  • Avoid touching your mouth, nose, and eyes frequently.


Coronavirus infections increase the chances of dangerous blood clots for up to six months. Several factors could be responsible. Regardless of the cause, you are exposed to problems, e.g., stroke, heart attack, and lung problems. If you are in active infection, have recently recovered, or are going for a vaccine, it is worthwhile to consult a doctor.

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