What is thrombosis?

Thrombosis occurs when blood clots block your blood vessels. There are 2 main types of thrombosis:

• Venous thrombosis is when the blood clot blocks a vein. Veins carry blood from the body back into the heart.
• Arterial thrombosis is when the blood clot blocks an artery. Arteries carry oxygen-rich blood away from the heart to the body.

What causes thrombosis?

Venous thrombosismay be caused by:

• Disease or injury to the leg veins
• Not being able to move around (immobility) for any reason
• A broken bone (fracture)
• Certain medicines
• Obesity
• Inherited disorders, or a greater likelihood of having a certain disorder based on your genes
• Autoimmune disorders that make it more likely your blood will clot
• Medicines that increase your risk of clotting (such as certain birth control medicines)

Arterial thrombosismay be caused by a hardening of the arteries, called arteriosclerosis. This happens when fatty or calcium deposits cause artery walls to thicken. This can lead to a buildup of fatty material (called plaque) in the artery walls. This plaque can suddenly burst (rupture), followed by a blood clot.

Arterial thrombosis can occur in the arteries that supply blood to the heart muscle (coronary arteries). This can lead to a heart attack. When arterial thrombosis occurs in a blood vessel in the brain, it can lead to a stroke.

What are the risk factors for thrombosis?

Many of the risk factors for venous and arterial thrombosis are the same.

Risk factors for venous thrombosis may include:

• A family history of a blood clot in a vein deep in the body, called a deep vein thrombosis (DVT)
• A history of DVT
• Hormone therapy or birth control pills
• Pregnancy
• Injury to a vein, such as from surgery, a broken bone, or other trauma
• Lack of movement, such as after surgery or on a long trip
• Inherited blood clotting disorders
• A central venous catheter
• Older age
• Smoking
• Being overweight or obese
• Some health conditions, such as cancer, heart disease, lung disease, or Crohn's disease

Risk factors for arterial thrombosis may include:

• Smoking
• Diabetes
• High blood pressure
• High cholesterol
• Lack of activity and obesity
• Poor diet
• Family history of arterial thrombosis 
• Lack of movement, such as after surgery or on a long trip
• Older age

What are the symptoms of thrombosis?

Each person’s symptoms may vary. Symptoms may include:

• Pain in one leg (usually the calf or inner thigh)
• Swelling in the leg or arm
• Chest pain
• Numbness or weakness on one side of the body
• Sudden change in your mental state

The symptoms of thrombosis may look like other blood disorders or health problems. Always see your healthcare provider for a diagnosis.

How is thrombosis diagnosed?

Your healthcare provider will take your medical history and give you a physical exam. Other tests may include:

• Ultrasound. This test uses sound waves to check the blood flow in your arteries and veins.
• Blood tests. These may include tests to see how well your blood can clot.
• Venography. For this test, a dye is injected into your veins. Then X-rays are taken to show blood flow and look for clots. The dye makes your veins easier to see on the X-rays.
• MRI, MRA or CT. The imaging procedure that is used will depend on the type of blood clot you have and where it is located.

How is thrombosis treated?

Your healthcare provider will create a treatment plan for you based on:

• Your age, overall health, and medical history
• How sick you are
• How well you handle certain medicines, treatments, or therapies
• If your condition is expected to get worse
• What you would like to do

Treatment may include:

• Blood-thinning medicines (anticoagulants)
• Thin tubes (catheters) to widen the affected vessels
• A wire mesh tube (stent) that holds a blood vessel open and stops it from closing
• Medicines to interfere with or dissolve blood clots

Your healthcare provider may advise other treatments.

What are the complications of thrombosis?

Thrombosis can block the blood flow in both veins and arteries. Complications depend on where the thrombosis is located. The most serious problems include stroke, heart attack, and serious breathing problems.

Can thrombosis be prevented?

You can reduce your risk of thrombosis by:

• Being active
• Getting back to activity as soon as possible after surgery
• Exercising your legs during long trips
• Quitting smoking
• Losing weight
• Managing other health problems such as diabetes, high blood pressure, and high cholesterol

Key points

• Thrombosis occurs when blood clots block veins or arteries.
• Symptoms include pain and swelling in one leg, chest pain, or numbness on one side of the body.
• Complications of thrombosis can be life-threatening, such as a stroke or heart attack.
• Treatment includes medicines that thin the blood or prevent clots, and using stents or catheters to open blocked vessels.
• Prevention includes being active, quitting smoking, losing weight, and managing other health conditions.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your provider tells you.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your provider if you have questions.