Thrombosis is when a blood clot, or thrombus, forms in a blood vessel. An embolus is when a clot, fat, air bubble, or other feature travels through blood vessels, with a risk of lodging elsewhere. Both can block blood flow and increase the risk of a heart attack or stroke.

This article will look at the differences between thrombosis and embolism. It will then compare these issues with aneurysms and deep vein thrombosis (DVT).

Finally, it will describe the symptoms, causes, diagnostic processes, and treatment options.

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Thrombosis happens when a blood clot, or thrombus, grows in blood vessels. This can reduce blood flow.

An embolus is any foreign material that travels within the body. If it becomes stuck and severely blocks the flow of blood, the issue is called an embolism.

a blood clota foreign material that movesa thrombus develops and reduces blood flowa blood clot or foreign object becomes stuck and reduces blood flow

The material of an embolus may be:

  • air
  • fat
  • blood clot
  • any other foreign material

Any blockage in a vein or artery can cause life threatening complications. One way that doctors classify these blockages is based on where they occur.

One of the most common types of embolism, for example, is pulmonary embolism. This happens when an embolus travels to the veins of the lungs, disrupting blood flow.

Like any blockage that interferes with blood flow to the heart, pulmonary embolism can lead to a stroke or heart attack.

Learn more about blood clots in the circulatory system here.

The symptoms of thrombosis and embolism can vary depending on the location and type of blockage.


This involves thrombosis in the deep veins. DVT can only become pulmonary embolism if the blood clot moves to the lungs. DVT often affects the pelvis and legs.

Symptoms of DVT may include:

Pulmonary embolism

A pulmonary embolism involves a blood clot or foreign material becoming trapped in the veins of the lungs, disrupting blood flow. It is a medical emergency, and some symptoms include:

A person may have stroke symptoms, such as numbness or weakness, or heart attack symptoms, such as intense chest pain and nausea.

Arterial thrombosis

Arterial thrombosis involves a blockage in an artery, which carries blood away from the heart. A vein, by contrast, carries blood toward the heart.

Symptoms of arterial thrombosis are similar to those of a blockage in a vein. They can vary but may include:

  • leg pain
  • leg or arm swelling
  • chest pain
  • numbness or weakness on one side of the body
  • mental changes

Learn more about where blood clot symptoms may develop.

An aneurysm happens when an artery wall weakens. This may cause the artery to balloon outward, twist, or weaken and bleed.

If this bleeding occurs, especially in the brain or from a major artery, an aneurysm can be fatal. However, not all aneurysms cause symptoms or require treatment.

The main difference between an aneurysm and embolism or thrombosis is that the latter two involve blockages, while an aneurysm involves damage to the artery wall.

Aneurysms can result from high blood pressure or smoking. A person can also be born with one.

Learn about aneurysm causes and treatment options here.

A blood clot forms when cells build up over a damaged blood vessel wall to protect it and stop it from bleeding.

A person could think of it as a scab for an internal wound. After the wound has healed, the blood clot dissolves. If this does not happen, the clot may break away and form a blockage.

In other cases, blood clots form at random.

DVT is the most common issue involving blood clots, and the following may increase the risk of developing it:

  • Injury: A serious injury to a deep blood vessel can cause a clot to form. For example, a person may have a higher risk after breaking a bone or having a car accident.
  • Pregnancy: Pregnant people are more vulnerable to blood clots. Also, very rarely, a life threatening condition called amniotic fluid embolism may develop.
  • Long periods of sitting or lying: People who are sedentary for long periods have a higher risk of developing an embolus or blood clot. This may include people who need bed rest, such as after surgery.
  • Cardiovascular health: The same things that increase the risk of heart disease, such as high blood pressure, advancing age, smoking, and obesity, can also increase the risk of a blood clot.
  • History: People with a family history of blood clots or other blockages may have a higher risk of developing one. Also, having one blood clot increases the likelihood of developing another.
  • Serious illness: People with lung disease, heart disease, certain types of kidney disease, and cancer may have a higher risk of a blood clot.

Embolism risk factors

Embolism refers to any material becoming trapped in a blood vessel, and there are several risk factors. Some include:

  • Air in a vein: Injecting air into a blood vessel can cause an embolus.
  • Pregnancy: Very rarely in pregnancy, amniotic fluid can enter the parent’s blood vessels, causing an amniotic fluid embolism.
  • Foreign materials in the body: Any foreign object, such as a splinter or bullet, could potentially enter the blood vessels and cause a blockage.
  • Infection: Certain infections can cause bacteria and other harmful pathogens to enter and block blood vessels.

A doctor may recommend testing, based on a person’s medical history and symptoms. The best test depends on where they suspect the blockage to be and the specific symptoms.

Some diagnostic strategies include:

  • blood tests
  • imaging tests, involving MRI or ultrasound scans, for example
  • pulmonary angiography, which involves inserting a catheter and a tool that sends back images into a vein to see the pulmonary veins better

Treatment for thrombosis usually involves blood thinners. Also, a surgeon may remove the blood clot, especially if it is very large or does not respond to medication.

Treatment for embolism depends on the type of blockage and its location. If a blood clot is involved, the doctor may recommend a blood thinner. This is generally what happens in cases of pulmonary embolism, unless the embolus is very large.

In certain circumstances, a doctor might need to insert a stent into a blood vessel to widen it. Also, a person may need supportive therapy, such as oxygen therapy.

Embolism and thrombosis can block important blood vessels and damage the organs that these blood vessels connect to.

Some potential complications may include:

Not all blood clots and emboli are preventable, but the following strategies may reduce the risk:

  • Receiving quality prenatal care: Certain risk factors, including heart health problems during pregnancy, may increase the risk of blockages, including blood clots and amniotic fluid emboli.
  • Having a heart-healthy lifestyle: Having obesity, smoking, and not having a cardiac diet may increase the risk of developing blood clots.
  • Becoming more active when possible: Try to avoid long periods of sitting or lying down. Take breaks from long stints of sitting at work. People who drive as a job should make frequent stops to stretch.

Anyone who suspects that they have a blood clot should receive immediate medical care, which can prevent life threatening complications.

A thrombus is a blood clot, and thrombosis is the formation of a clot that reduces blood flow.

An embolus is any foreign material that moves with blood flow. An embolism happens when an embolus severely blocks the flow of blood.

A person cannot distinguish one from the other based on their symptoms. Anyone who may be having one of these health issues should receive immediate medical attention. Make sure that the doctor is aware of any risk factors for blood clots or other cardiovascular health problems.