Blood clots: symptoms, types and when to get care

Medical disclaimer: This page is general health information for education only. It is not medical advice and is not a substitute for diagnosis or treatment by a qualified health professional. It has not been reviewed by a clinician. In an emergency, call 911 or your local emergency number.

A blood clot that forms in the wrong place can block blood flow to a leg, a lung, the heart or the brain. This page covers the main types, symptoms by location, when to call 911, risk factors, and how clinicians test for and treat clots. It is part of our library of health conditions.

What is a blood clot?

A blood clot is a mass of blood that forms when platelets, proteins and cells in the blood stick together.

Your body normally uses clots to stop bleeding. Problems start when a clot forms inside a blood vessel without a good reason, or does not dissolve when it should, as MedlinePlus explains in its overview of blood clots.

Clots can form in blood vessels in the limbs, lungs, brain, heart and kidneys. This section does not cover bleeding disorders.

Types of blood clots: DVT, PE and arterial clots

The main types are deep vein thrombosis, pulmonary embolism and clots in arteries.

• Venous thromboembolism (VTE) is the term for blood clots in the veins. Veins carry blood back to the heart.
• Deep vein thrombosis (DVT) is a clot in a deep vein, most often in the lower leg, thigh or pelvis. DVT can also occur in the arm.
• Pulmonary embolism (PE) happens when part of a clot breaks off and travels to the lungs. PE can be life-threatening.
• Arterial clots block arteries. Clots in arteries can cause an ischemic stroke or a heart attack.

These definitions follow the CDC overview of blood clots. Up to 900,000 people in the United States are affected by VTE each year. An estimated 60,000 to 100,000 Americans die of VTE each year, according to CDC data on blood clots.

This page does not cover heart attack or stroke in detail. Heart attack symptoms are covered on our page about heart attack symptoms in women.

Blood clot symptoms by location

Blood clot symptoms depend on where the clot is. A leg clot often causes swelling and pain, while a lung clot often causes sudden shortness of breath.

Sources: the CDC list of DVT and PE signs and MedlinePlus pages on arterial embolism and blood clots.

About half of people with DVT have no symptoms at all. Sometimes a vein clot causes no symptoms until serious complications develop. A lack of symptoms does not rule out a clot. This table is not a way to diagnose yourself.

Emergency signs: when to call 911

Call 911 if you have sudden trouble breathing, chest pain, coughing up blood or fainting. These can be signs of a pulmonary embolism.

MedlinePlus advises you to go to the emergency room or call 911 if you have symptoms of a pulmonary embolus. It gives the same advice for symptoms of a clot blocking an artery.

Call 911 right away for any of these:

• Sudden shortness of breath, at rest or with activity
• Chest pain that may be sharp, stabbing or burning
• Coughing up blood
• Dizziness, lightheadedness or fainting
• A cold, pale, painful arm or leg with a weak or missing pulse
• Trouble speaking or a severe headache

Call your health care provider right away if you notice leg swelling, pain, warmth or redness without these emergency signs. This list does not replace the judgment of a 911 dispatcher or emergency team.

Who is at higher risk for blood clots?

Your risk of a blood clot rises after surgery or injury, during long periods without moving, with more estrogen, and with some long-term illnesses.

The CDC lists these risk factors for blood clots:

• Injury to a vein from a fracture, severe muscle injury or major surgery, especially of the belly, pelvis, hip or legs
• Slow blood flow from being confined to bed in the hospital, from illness or after surgery
• More estrogen from estrogen-containing birth control, hormone replacement therapy or pregnancy, with risk lasting up to 3 months after giving birth
• Long-term illnesses such as heart disease, lung disease, cancer and its treatment, and inflammatory bowel disease
• A past DVT or PE, an inherited clotting disorder or a family history of DVT or PE
• Older age, overweight or obesity, and a catheter in a central vein

The chance of a clot increases even more when you have more than one risk factor at the same time. The chance of VTE nearly doubles every 10 years after age 40. The chance of a clot is highest in the first 3 months after surgery, according to NHLBI information on VTE causes. DVT can also develop during a flight longer than 4 hours.

Some conditions covered elsewhere on this site raise clot risk. Heart disease is on the CDC list. NIDDK lists blood clots as a complication of nephrotic syndrome, a kidney disorder. Having a risk factor does not mean you will get a clot.

How clinicians diagnose blood clots

Clinicians usually diagnose DVT with an ultrasound of the leg and PE with a CT scan of the lung arteries.

• Duplex ultrasound uses sound waves to look at blood flow in the veins. It is the standard imaging test for DVT.
• D-dimer blood test measures a substance released when a clot breaks up.
• CT pulmonary angiography (CTPA) takes pictures of the blood vessels in the lungs. It is the standard imaging test for PE.
• Ventilation perfusion (V/Q) scan measures air flow and blood flow in the lungs.
• Pulmonary angiography uses a thin tube called a catheter and is the most accurate test for PE.

These descriptions follow the CDC guide to testing for blood clots. Which tests you get depends on your symptoms and health history. For example, MRI is usually saved for certain patients, such as pregnant women. A home check or a symptom quiz cannot confirm or rule out a clot.

How clinicians treat blood clots

Clinicians most often treat DVT and PE with anticoagulants, commonly called blood thinners. These keep clots from growing and stop new ones from forming.

The NHLBI describes these treatment options:

• Anticoagulants can be given as shots, pills or through a vein. How long you take them depends on the medicine and on what caused the clot.
• Thrombolytics, or clot busters, dissolve clots. They are used for large clots that cause severe symptoms or serious complications, such as PE. The CDC notes they carry a higher risk of bleeding.
• Catheter procedures use a thin, flexible tube to reach a clot in the lung or leg to break it up or deliver medicine.
• A vena cava filter can catch clots before they reach the lungs in people who cannot take blood thinners. It does not stop new clots from forming.

For clots in arteries, MedlinePlus notes that treatment can include anticoagulants, antiplatelet medicines, clot-dissolving medicines and surgery to restore blood flow. This page does not give medicine names or doses. Do not start, stop or change a blood thinner on your own.

Some people have problems after a clot. About 1 in 3 people with a VTE will have another one within 10 years. One third to one half of people with DVT develop long-term swelling, pain or skin changes in the limb, according to CDC data.

Questions to bring to your appointment

Bringing written questions helps you use your visit well. Our guide on how to prepare for an appointment has more tips. These questions are a starting point, not a complete list.

• Do my symptoms need testing for a blood clot, and which tests do you recommend?
• Which of my health conditions, medicines or recent events raise my clot risk?
• How long will I need treatment, and what side effects or bleeding signs should I report?
• What activity, travel or work changes should I make while I recover?
• What is my chance of another clot, and how can I lower it?
• Which symptoms mean I should call 911 instead of calling your office?