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EspañolWhat causes blood clots? Diagnosis, prevention, and treatment
Overview: What are blood clots?
Blood clots are the body’s defense mechanism against bleeding. They usually occur when some body part is injured, like a cut or bruise. Cells in the blood called platelets stick together and form a solid mass at the injury preventing more bloodloss. However, when a blood clot forms within the bloodstream, it can pose a serious health threat called a “thrombus.” If the blood clot breaks loose from where it formed, it can travel through the bloodstream and get stuck in a further downstream blood vessel blocking blood flow. When a bloodclot moves this is called an “embolus.” A blood clot can block blood flow through a vein or artery. If it blocks a vein, blood will pool behind the clot, causing swelling and pain. A clot blocking an artery prevents oxygen from getting to tissues. If the tissues are deprived of oxygen long enough those tissues die. Heart attacks and strokes are two examples of blood clots blocking blood flow and oxygen to a vital organs (the heart and brain respectively). For this reason, blood clots are the most common cause of death in the United States and other developed countries.
Key takeaways:
Blood clots are a common health condition affecting anyone regardless of age, sex, race, or ethnicity.
Blood clots are caused by injury, surgery, genetic disorders causing the blood to be thicker than normal, some cancers, medication side effects, pregnancy, immobility, heart rhythm abnormalities like atrial fibrillation, heart failure, and blood vessel problems.
Risk factors for blood clots include obesity, smoking, family history of blood clots, pregnancy, cancer, use of certain medications, and sitting or lying down for long periods (like when sedentary after a surgery, illness, or while on a long flight).
Symptoms of blood clots include swelling, pain, and skin color changes. Other symptoms will depend on where the blood clot is located. Oftentimes, blood clots have no symptoms.
Blood clots usually require a medical diagnosis.
Blood clots generally do require treatment. A blood clot typically resolves with blood thinners in three or more months. Treatment is directed at dissolving the blood clot, and surgery typically eliminates the blood clot by the end of the procedure. Blood thinners often help the body stabilize the blood clot so that parts of the blood clot do not move (and become and embolus) and the body dissolves the blood clot on its own over time.
Treatment of blood clots may include blood thinners, thrombolytics, breaking up blood clots through a catheter, or surgery. Read more about blood clot treatments here and pulmonary embolism treatments here.
Blood clots are preventable by regular checkups, weight loss, a healthy diet, drinking fluids, exercising, and avoiding prolonged sedentary periods. Some blood clots are not preventable like when you have a heart arrhythmia that you were unaware of or you have a genetic predisposition to blood clots, but have not had one yet.
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What causes blood clots?
Causes of blood clots fall into three categories:
Hypercoagulability: some medical or genetic conditions cause blood clots to form more easily than they would in normal blood
Endothelial damage: injury or damage to the inner wall of blood vessels can cause blood clots to form at that injury
Blood stasis: blood flow can sometimes slow down or even stop somewhere in the circulatory system, making blood clots more likely to form
Any of these causes of blood clots can bring about a blood clot. However, blood clots usually form in the presence of more than one of these causes. For instance, someone with hypercoagulable blood might get a blood clot because the blood slows down in one part of the circulatory system.
The most common causes of hypercoagulability include:
Genetic disorders
Medications, particularly oral contraceptives or estrogen replacement therapy
Pregnancy
Injury
Surgery
Chronic inflammation
Cancer
Infection
Peripheral vascular disease
The most common causes of blood vessel damage are:
Injury
Surgery
Catheters
High blood pressure
High cholesterol
The most common causes of blood stasis are:
Heart rhythm abnormalities (also called arrhythmias like Atrial fibrillation)
Immobility, such as sustained bed rest
Pregnancy
Previous blood clots
RELATED: Blood clots during pregnancy: symptoms and prevention
Risk factors for blood clots
Since there are three major causes of blood clots, several risk factors are related to one or more of these causes. These include:
A family history of blood clots
Chronic inflammatory conditions such as rheumatoid arthritis and inflammatory bowel disease
Tobacco use
Obesity
Use of certain medications, such as birth control pills
Hormone replacement therapy
Pregnancy
Infections such as COVID-19
Cancer
Immobility or sedentary lifestyle
Venous insufficiency (weak veins in the legs)
Heart problems
Blood vessel problems
Injury
Surgery
Catheter placement
Are blood clots serious? When to see a doctor
A blood clot in a vein or artery is a serious and potentially life-threatening medical condition. See a doctor as soon as possible if there are symptoms of a blood clot in a vein located in the leg or arm, called deep vein thrombosis (DVT) or venous thromboembolism (VTE):
Swelling in a leg or arm
Pain or cramping in a leg or arm
Skin color changes in the affected limb
A blood clot blocking an artery or abdominal vein is a medical emergency. Immediately go to an emergency room or call 911 if you have symptoms such as:
Heart symptoms: chest pain, chest heaviness, pain or discomfort in the shoulders or arms, shortness of breath, and lightheadedness
Lung: sharp chest pain, coughing up blood, dizziness, shortness of breath, racing heartbeats, and difficulty breathing
Brain: sudden numbness somewhere on the body, drooping in the face, confusion, difficulty talking, vision problems, dizziness, balance problems, and headache
Abdomen: severe abdominal pain, bloating, nausea, bloody vomit, swelling in the legs, and confusion
RELATED: Pulmonary embolism symptoms: what are the early signs of pulmonary embolism?
How are blood clots diagnosed?
Healthcare professionals approach diagnosis based on the type of blood clot. A medical history will help a healthcare provider determine where the blood clot is and what risk factors may be responsible. The clinician will usually score symptoms and risk factors to determine if further workup is required.
If so, several tests may be required depending on the type of blood clot and where it’s located. These include blood tests to spot chemical markers of a blood clot (a d-dimer test) in addition to scans or other tests:
An electrocardiogram (ECG) for the heart
Pulmonary angiogram or ventilation-perfusion scan (V/Q scan) for the lungs
A brain CT scan or MRI for stroke
CT angiography for an abdominal blood clot
Contrast venography for deep vein thrombosis
Are blood clots hereditary?
Some people are born with inherited medical or genetic conditions that make their blood form clots more readily than normal. These conditions include Factor V Leiden mutation and prothrombin G20210A mutation. Additionally, some people are born with certain deficiencies of Protein C, Protein S, and prothrombin III, a blood clotting protein. These inherited conditions also make the blood more likely to form abnormal blood clots.
Are blood clots curable?
Blood clots are treatable. They do eventually dissolve on their own, but doctors may want to stabilize the blood clot or at times speed up the process. If a blood clot is in a vein, it will probably be treated by a specialist in blood vessels called a hematologist. If a blood clot is in an artery, other specialists may be involved such as a cardiologist, neurologist, or pulmonologist (lung doctor).
Treatments may include:
Drugs that prevent blood clots from forming called anticoagulants
Drugs that dissolve blood clots called thrombolytics
Placing thrombolytic drugs directly on the blood clot using a catheter, a procedure called catheter thrombolysis
Surgical removal of the blood clot
For venous blood clots, a filter called a vena cava filter may be placed in the vein entering the heart to prevent the blood clot from entering the lungs. This may be done if blood clots continue to form despite the patient taking blood thinners
How to prevent blood clots
Healthcare professionals consider blood clots among the most preventable blood problems because many risk factors are related to lifestyles. To lower the risk of blood clots:
Get regular checkups
Lose weight and maintain a healthy weight
Stop smoking
Eat a healthy diet
Exercise
Wear compression stockings
Do not sit or lie down for long periods—regularly stand up and move around
If you have a condition like high blood pressure, high cholesterol, or diabetes, follow the lifestyle advice given by healthcare providers and take the medications as instructed
Most importantly, get medical help at any sign of a blood clot
For people at risk, it’s imperative to learn the signs and symptoms of a blood clot, particularly symptoms of a clot in blood vessels of the heart, lung, brain, or abdomen. These are medical emergencies, and the outlook is best when they are treated as soon as possible. Better yet, take positive measures to reduce the risk. Sit down and discuss with your primary care provider if you have risk factors for a blood clot. Lifestyle changes can help prevent a frenzied and frightening visit to an emergency room.
FAQs about blood clot causes
How do I prevent blood clots?
Many risk factors for blood clots are lifestyle habits such as diet, overweight, smoking, and sitting around too much. The first steps to prevent blood clots are to lose weight, stop smoking, and start exercising, even if exercise means walking more than usual. Next, manage chronic conditions such as diabetes, high blood pressure, high cholesterol, or other chronic diseases by taking your prescribed medications and making suggested lifestyle changes. However, you will need to change what you eat at every step. Unfortunately, there is no one perfect diet to prevent blood clots. The best diet will depend on your particular mix of risk factors for blood clots.
RELATED: The best diets for 15 common health conditions
Where do blood clots usually start?
A blood clot can start anywhere in the body. It depends on several factors, but usually, blood clots form in places where the flow of blood is slowed down or static. For most people, slowed blood flow happens in the legs. It’s not uncommon for the veins in the legs to lose the ability to send all the blood back out of the legs. That’s where varicose veins come from. Called venous insufficiency, weak veins cause blood to pool up in the legs, providing just the right circumstances for a blood clot to form. However, some people have heart problems such as atrial fibrillation, heart failure, or heart valve problems (mitral valve stenosis) that can cause blood to pool up in the heart, again, creating an environment conducive to blood clots.
RELATED: What causes afib? Diagnosis, prevention, and treatment
Do blood clots happen suddenly?
Blockages due to blood clots are usually unexpected and sudden events. This includes blood clots in the leg (deep vein thrombosis), in the heart (arterial thrombosis), in the brain (stroke), and in the lungs (pulmonary embolism). Symptoms come on suddenly, unexpectedly, and sometimes with great intensity.
What’s next? Additional resources for people with blood clots
Test and diagnostics
Blood clotting disorders (hypercoagulable state), Cleveland Clinic
Pulmonary embolism symptoms and diagnosis, American Lung Association
SMV Thrombosis, Cleveland Clinic
Thrombosis, StatPearls
Treatments
Blood clots, American Society of Hematology
Deep venous thrombosis and pulmonary embolism: current therapies, American Family Physician
Scientific studies and clinical trials
The coagulation system in host defense, Research and Practice in Thrombosis and Haemostasis