What is a Blood Clot?

Updated October 2024

A blood clot occurs when blood changes from a liquid to a thick, semi-solid substance inside a blood vessel. Blood clots can block blood from getting to parts of your body. Clotting is part of coagulation, a normal process that helps stop bleeding if you get hurt.

When a blood vessel is injured, it narrows to stop blood from leaking out. Platelets, a special type of blood cell, go to the injury site and stick together, forming a plug and ultimately creating a clot that seals the injury.

After the clot forms, the body’s immune system repairs the injury, and other cells break down the clot. But sometimes, clots form when they shouldn’t, or they don’t dissolve properly.

What is deep vein thrombosis (DVT)?

DVT is a blood clot that occurs in a deep vein. Deep veins are found in your muscles and alongside bones. DVTs can form in any deep vein, but are more likely to form in the calf, thigh, or pelvis areas. In a DVT, a clot blocks blood flow in the vein, leading to pain and swelling around the clot. Clinicians typically use an ultrasound to diagnose DVTs.

What Causes Blood Clots in the Legs?

Blood clots in the legs usually happen for three reasons:

1. Stasis (Stay-sis): Blood should keep moving all the time in your body,  but sometimes, blood can slow down or even stop in certain areas. That’s called “stasis.” When blood is in stasis, it can cause problems like blood clots because it’s not moving the way it should.

2. Hypercoagulability (Hyper-coag-you-la-bil-ity): Hypercoagulability means that your blood has an increased tendency to form clots. Genetic disorders, taking certain medications (like birth control pills or hormone therapy) , or conditions like cancer are all things that can make your blood more likely to clot

3. Blood Vessel Injury: Damage to blood vessels can occur during surgery or result from inflammation, fractures, or trauma injuries.

What is pulmonary embolism (PE)?

A PE occurs when a blood clot breaks off and travels to the lungs, blocking blood flow. This type of clot reduces oxygen in the blood and makes it hard to breathe. Most PEs come from DVTs in the legs or pelvis and can be life-threatening.

What Does a Blood Clot Feel Like?

The symptoms of a blood clot depend on where the clot is in your body and how much blockage there is. 

Common DVT symptoms:

• Pain or discomfort in the affected area, sometimes described as aching, throbbing, or cramping
• Skin changes like discoloration or thickening
• Swelling, itchiness, or warmth near the clot

Common PE symptoms:

• Sudden shortness of breath
• Rapid or irregular heartbeat
• Coughing up blood
• Chest pain

If you have any of these symptoms, seek emergency medical help right away.

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Who’s at Risk for a Blood Clot?

Some people are more likely than others to develop blood clots. Those who get a blood clot usually have more than one risk factor. The more risk factors you have, the higher your chance of developing a blood clot. Risk factors include:

• Surgery
• Obesity
• Smoking
• Diabetes
• Infections
• Pregnancy
• Major trauma
• Atrial fibrillation, a type of irregular heartbeat 
• Family history of clots
• Limited physical activity
• Cancer and chemotherapy
• Inflammatory or autoimmune disease
• Genetic or acquired clotting disorders
• Plaque build-up in arteries or atherosclerosis
• Estrogen-containing birth control pills and hormone replacement therapies

Treating Blood Clots

Treating blood clots as soon as possible is important to prevent complications. The kind of treatment you get depends on how serious the blood clot is and where it is in your body. Treatments may include:

• Blood thinners, also called anticoagulants (anti-coag-you-lents) stop clots from growing bigger and help prevent new clots from forming. Most people take blood thinners for at least 3-6 months after having a blood clot, depending on the situation. Some people may need to take these medicines for years if they have certain risks that could lead to more blood clots.
• Thrombolytics: Thrombolytics are strong medicines that break up big clots. They are given by a clinician who watches you closely.
• Catheter-guided clot removal: During this procedure, a clinician uses a thin, flexible tube to reach the blood clot and then uses either a device or medicine to break up the clot.
• Filters: A vena cava filter can help people with DVT who can’t take blood thinners. The filter is placed in a large vein called the vena cava. It catches blood clots before they travel to the lungs and cause a PE. However, the filter doesn’t stop new blood clots from forming.

Preventing Blood Clots

There are ways to lower your chance of getting blood clots:

• Stop smoking.
• Maintain a healthy weight.
• Decrease the amount of salt in your diet.
• Stay hydrated by drinking plenty of fluid while awake.
• Try to avoid sitting or standing for more than one hour.
• If traveling or sitting for a long time, take breaks to get up and move around.
• Use compression stockings to help blood return to the heart from your legs.
• Keep moving by doing exercises that keep blood flowing, like walking.
• When lying down, keep your legs elevated above the level of your heart.
• Take blood thinners as directed by your doctor or healthcare team.