Thrombosis occurs when a blood clot blocks your blood vessels. There are different types, and it can be serious without quick treatment.

Thrombosis is a medical condition where a blood clot inside either a vein or an artery blocks the flow of blood around your body.

It can happen when a blood vessel gets injured, and the body forms a clot to prevent blood loss, but it can also happen with no injury to the blood vessel. When a blood clot, or a piece of a clot, breaks free and travels around the body, it’s known as an embolus.

There are several types of thrombosis, and you can learn more about them here.

There are two main types of thrombosis: arterial and venous.

With arterial thrombosis, a thrombus develops in an artery ― the type of blood vessel that carries oxygenated blood away from the heart to elsewhere in the body. The most common cause of arterial thrombosis is atherosclerosis, which occurs when you have a buildup of plaque on the walls of your arteries.

As the arteries narrow and begin to harden, the risk of arterial thrombosis can increase.

With venous thrombosis, a thrombus develops in a vein ― the type of blood vessel that carries deoxygenated blood back to the heart.

What are the subtypes of venous thrombosis?

There are two main subtypes of venous thrombosis: deep vein thrombosis (DVT) and pulmonary embolism (PE).

DVTtends to occur in your leg or pelvis, where it’s known as lower-extremity thrombosis, but it can occur in your arm or shoulder, where it’s known as upper-extremity thrombosis. Deep veins sit far inside your body, further away from your skin.

Paget-Schroetter syndrome is a type of DVT that, while rare, can affect young people who play sports that use their upper arms. The vein gets squeezed by the muscles around it, which can become aggravated with overuse.

A PE occurs when a blood clot formed elsewhere ― often in a deep vein in your leg ― breaks off and travels through the bloodstream to your lungs. It can block the flow of blood to your lungs, not only affecting your lungs but other organs too, as your lungs won’t be able to supply oxygen to them as effectively. PE can be fatal when there’s a large clot, or you have more than one.

There’s also femoral vein thrombosis ― a clot in the long vein in your thigh ― which can sometimes occur if you’ve had DVT before.

Other types of venous thrombosis include the following:

What is the difference between a blood clot and a thrombosis?

A blood clot is a clump of blood that forms when your blood hardens from a liquid to a solid. With thrombosis, the blood clot forms in a vein or artery ― this is called a thrombus.

All thrombi are blood clots, but not all blood clots are thrombi.

Learn more about the difference between a thrombosis and an embolism here.

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What is the most common type of thrombosis?

DVT is the most common type of thrombosis that can cause serious complications. This type of thrombosis usually occurs in the leg or pelvis but can occur in the arm or shoulder.

What is the rarest type of thrombosis?

Many types of thrombosis are rare. Jugular vein thrombosis, often due to intravenous substance use, is rare, as is cerebral venous sinus thrombosis — a type of stroke — and Paget-Schroetter syndrome, a rare form of DVT.

What is the most life threatening type of thrombosis?

PE is the most life threatening type of thrombosis. It can be fatal without prompt treatment, as the blood clot travels to your lungs. Here, it can block blood vessels and keep oxygen from getting to your tissues and organs.

Other types of thrombosis

The human cardiovascular system is vast. As such, there are many different types of thrombosis that this article has just scratched the surface of. Other types include, but aren’t limited to:

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Many types of thrombosis can occur in different areas of the body, but they’re all caused by blood clots.

If you’re concerned that you might have a type of thrombosis, it’s best to speak to your doctor. If you’re experiencing severe symptoms, call 911 or your local emergency services, or get somebody to take you to an emergency room.

When you treat thrombosis quickly, you reduce the chance of it becoming life threatening.