Blood clots are the body’s way of stopping blood loss. If you cut your finger, the blood in the area of injury turns from liquid to solid, stopping the flow from your finger and paving the way for healing.
Clots are formed by blood cells and other factors in the blood. While most blood clots serve a helpful purpose, others cause problems. Blood clots aren’t a problem unless they block the flow of blood where it belongs. Normally, blood carries oxygen to all parts of the body. Blood clots can keep blood and oxygen from reaching parts of the body, and without adequate oxygen, body parts can be damaged. Heart muscle or brain tissue that doesn’t get enough oxygen, for instance, begins dying, and that hurts the functioning of the body.
A DVT is a deep vein thrombosis. The word thrombosis means clot, so a deep vein thrombosis, or DVT, is a blood clot that forms in a vein deep inside the body, usually the leg, that blocks important blood flow. These blood clots can break loose and travel to other parts of the body. A blood clot that travels to the lungs and blocks the flow of blood and oxygen to the lungs is called a pulmonary embolism, or PE. A PE is a potentially life-threatening event.
DVT and PE affect an estimated 350,000 to 600,000 Americans each year, contributing to at least 100,000 deaths annually. Most occur in people who have other illnesses or are recovering from surgery or a serious accident.
The best way to avoid being harmed by a DVT or PE is to know the symptoms. Timely diagnosis and treatment can help people avoid the most damaging outcomes.
DVTs usually occur in the legs. The most common symptoms of DVT include:
- Swelling in the affected leg
- Pain in the leg (may feel like cramping in the calf)
- Warmth in the affected area
- Redness or other changes in skin color, such as the skin turning more pale or more blue than usual
A DVT can also occur without any noticeable symptoms.
Symptoms of a PE, a blood clot that has traveled to the lungs, include:
- Difficulty breathing
- Sharp chest pain that worsens after taking deep breaths
- Coughing up blood
- Light-headedness, fainting, and unconsciousness (for very large clots)
Symptoms of a PE can occur very suddenly and without warning. PE symptoms always require prompt medical assessment.
Many different things can cause DVTs. Some of the most common causes and contributing factors include:
- Sitting for long periods of time, such as during long-distance travel or prolonged bed rest. When your body remains in one position for a long time, blood is more likely to pool and clot.
- Inheriting a blood-clotting disorder. Sometimes tendency to clot excessively runs in families. Factor V Leiden thrombophilia is an example of a disorder that increases the likelihood of developing harmful blood clots and DVTs.
- Injury or surgery. Anytime the inside lining of a blood vessel is damaged, blood is more likely to clot.
- Pregnancy. Increased hormone levels during pregnancy make the blood prone to clotting. Pregnancy also decreases blood flow to the lower legs, increasing the risk of DVT. The risk of developing a DVT remains elevated in the first 6 weeks after birth.
- Estrogen use, including the use of oral contraceptives (birth control pills). Hormone therapy treatment and birth control pills both increase the risk of blood clots and DVTs. Smoking further increases this risk. (That’s why birth control pills are not recommended for women who smoke.)
- Cancer. Researchers and clinicians have long noticed a link between certain types of cancers and blood clots. People with cancers of the brain, ovaries, pancreas, colon, stomach, lung, kidney, or liver are at increased risk of developing DVTs. Lymphoma and leukemia, two types of blood cancer, also increase the risk of DVT.
- Advanced age. Most DVTs occur in people over the age of 60, though they can occur at any age.
- Obesity. People who are obese face more than twice the risk of developing a DVT or PE than people who are not obese. Women who are obese and take birth control pills have an even higher risk of DVT.
- A history of DVT or PE. A previous DVT or PE dramatically increases the risk of a subsequent DVT.
Some of the most significant risk factors for DVT are:
- Being inactive for long periods. When you stay in bed after surgery or a serious illness or you sit for a long time on a flight or car trip, blood pools in your legs, increasing the likelihood of a DVT.
- Recent surgery that involved the legs, hips, belly, or brain. Major surgeries (think of a C-section) increase the risk of DVTs more than minor surgery (such as removal of the tonsils).
- Diseases such as cancer, heart failure, stroke, or a severe infection.
- Blood-clotting disorders.
Some things that increase your risk of DVT—such as an inherited blood-clotting disorder or advanced age—are out of your control. Other risk factors—such as smoking—are in your control. You can decrease your risk of developing a DVT by maintaining a healthy weight, staying active, and not smoking. If you’re a woman of childbearing age, you might want to consider nonhormonal methods of birth control, especially if you have other risk factors for DVT.
A PE is the most serious complication of DVT. PE occurs when a DVT travels through the bloodstream from the leg to the lungs. The clot can lodge in the pulmonary artery, the main blood vessel supplying oxygen to the lungs. A PE can cause difficulty breathing and an irregular heartbeat. A clot may be so large that it blocks the flow of blood from the heart, leading to heart failure, shock, and death.
The signs and symptoms of a PE include:
- Sudden shortness of breath and rapid breathing, even when resting
- Coughing up blood
- Chest pain
- Sudden rapid heart rate
A PE is a medical emergency. If you or anyone you know experiences any of these symptoms, call 911 and seek emergency medical treatment immediately. Prompt medical treatment can dissolve the blood clot and restore blood flow and oxygen delivery to the lungs.
Another complication of DVT is called postthrombotic syndrome. Postthrombotic syndrome is lasting damage to the leg. If a clot stays in a vein for too long, it can damage the vein and allow blood to pool in the leg. Signs and symptoms of postthrombotic syndrome include:
- Darkened skin color
- Skin ulcers
- Varicose veins
- Recurring DVT or PE
Approximately two out of three people who develop a DVT will also develop postthrombotic syndrome.
Preparing for your Appointment
Whether you go the emergency room or a doctor’s office, you should be prepared to talk about your medical history and current symptoms. If possible, gather the following information before you go:
- Past medical history. Do you have any medical problems? How are they treated? Have you had any surgeries in the past? What kind?
- List of medications. Make a list of all medications, supplements, and vitamins that you take. Better yet, bring the bottles with you to your appointment. That way, your health-care provider can see exactly what you’re taking, and in what doses.
- Family history. Has anyone in your family ever had a DVT or PE? Is there a family history of a blood-clotting disorder?
- Current symptoms. When did you first notice symptoms of a DVT or PE? Is the leg affected? When did your symptoms occur? Have your symptoms changed over time? Has anything provided relief?
Tests and Diagnosis
Your health-care provider will ask you about your symptoms and conduct a thorough physical examination. If a DVT is suspected, you’ll probably undergo an ultrasound. A technician will run an ultrasound probe down your leg, pressing gently, to look for clots.
Your health-care provider may also order blood tests. A D-dimer test is often done in people with a suspected clot. If the test result is negative (normal), you probably do not have a blood clot. A positive (abnormal) test result does not always mean a blood clot is present, however. Additional testing, such as an ultrasound, is usually needed to confirm or rule out a blood clot.
Blood tests can also be used to look for inherited blood-clotting disorders or other abnormalities that might increase the tendency to clot.
If your symptoms suggest a PE, your health-care provider will take steps to support your breathing and move quickly to see if a blood clot is responsible for your discomfort. Tests for PE include:
- Lung scan (also known as ventilation-perfusion lung scan or VQ scan). This is actually a combination of two tests: when to look at ventilation (how well air is moving through your lungs) and another that looks at perfusion, or blood flow, to the lungs.
During the ventilation scan, you’ll inhale a special gas through a mask. A scanner will track the flow of the gas through your lungs. Before the perfusion exam, a health-care provider will inject a radioactive solution into your veins. During the scan, you’ll lay underneath a special scanner while it tracks the flow of the solution through the pulmonary arteries that carry blood through the lungs.
- CT scan (also known as a CAT scan). A CT scan can also be used to look for a PE. Before a CT scan, a health-care provider will inject special dye into a vein in your arm. The dye will help the blood vessels in your legs and lungs and show up on the CT scans. You’ll lie on a table during the test while a scanner rotates around you, taking pictures from many angles. A CT scan only takes a few minutes.
Treatment and Drugs
The primary goal of treatment is to prevent the complications that can occur with DVT. Because DVTs that occur below the knee do not usually travel to other parts of the body, health-care providers often monitor them with ultrasounds that are repeated over time. At the same time, your health-care provider will work to uncover the cause of the clot and may suggest medical treatment to address the cause.
Very big DVTs and PEs are sometimes treated with clot-busting medication. The medication breaks up the clot, restoring blood and oxygen flow and decreasing the risk of serious complications.
Anticoagulation therapy, the use of medication to thin the blood and to prevent clotting, is used to treat all DVTs and PEs. Its major use is to prevent new clots from forming while allowing the body to dissolve the clots that exist.
Different anticoagulants (medications that thin the blood and prevent clotting) may be prescribed. Some work quickly. Others take time to build up in the blood and become effective.
Heparin and low-molecular weight heparin (enoxaparin/Lovenox) are used in hospitals and health-care settings to thin the blood soon after a DVT or PE is diagnosed. Heparin may be given intravenously or injected as a shot just beneath the skin, whereas low-molecular weight heparin (enoxaparin/Lovenox) is given as a shot beneath the skin.
At the same time one of these medications is started, patients may begin treatment with an oral anticoagulant, a pill that is taken by mouth. Oral anticoagulants take time to reach therapeutic levels in the blood. A therapeutic level of anticoagulant in the blood means that the blood is just right—not too thin and not too thick. When the anticoagulant is therapeutic, patients may stop heparin or low-molecular weight heparin treatment. They continue treatment with the oral anticoagulant.
The most common oral anticoagulant is warfarin. Warfarin has been used in humans since 1954 and is routinely used to treat and prevent DVTs and PEs. It takes time to find the proper dose of warfarin. If you start treatment with warfarin, your health-care provider will carefully monitor your blood with blood tests and tweak your dose of warfarin up or down to keep your blood “just right.”
Some people can’t take warfarin or are unable to return to their health-care providers’ offices for blood tests and dosage adjustments. If you are unable to take warfarin for any reason, you may be a good candidate for treatment with one of the newer anticoagulants.
- Dabigatran is an oral blood thinner that is taken as a pill. It does not require regular blood testing and is FDA-approved to prevent stroke in patients with an irregular heartbeat (atrial fibrillation).
- Rivaroxaban was approved by the FDA in 2012. It comes in pill form and does not require regular blood testing.
- Apixaban was also FDA-approved in 2012. Like dabigatran and rivaroxaban, it comes in pill form and does not require regular blood tests.
All blood-thinning medications increase the risk of bleeding. If you notice any abnormal bleeding—cuts that bleed profusely, blood in your bowel movements, heavier-than-normal menstruation, blood-tinged or blackish sputum (phlegm), or vomit—let your health-care provider know ASAP. About 1% to 2% of people taking blood thinners will develop serious bleeding that may require a blood transfusion and interruption of blood-thinning treatment.
Most people stay on anticoagulant medication for 3 to 6 months after a DVT or PE. Some people at high risk of repeated DVT and PE may be prescribed anticoagulants for life.
Some patients cannot take blood-thinning medication. Patients who have had a severe injury may be at high risk of serious bleed with blood thinners. Others may have a PE even when taking medications to prevent them. In these situations, a doctor may place a filter in the inferior vena cava, the major vein leading from the legs to the heart, to catch clots and prevent them from reaching the lungs.
Lifestyle and Home Remedies
You can help decrease your risk of developing DVTs. If your health-care provider suspects you are at increased risk of a DVT or blood clot for any reason—genetics, upcoming surgery, limited movement—he or she may recommend:
- Preventive treatment with blood-thinning medication.
- Elastic compression stockings. These stockings, worn on the legs, provide gentle, graduated pressure to keep blood from pooling in the legs. Compression stockings are custom-fit and obtained by prescription. Stockings should be put on after waking and worn throughout the day; they can be removed to bathe and at bedtime.
- Movement breaks on long trips. The overall risk of developing a DVT while traveling is low, although it increases on trips over 4 hours long, especially in long airplane or car trips. You can decrease this risk by moving and flexing your legs and periodically walking around. If you’re at high risk of developing a DVT or blood clot, your health-care provider may recommend that you wear compression stockings while traveling.
Because blood-thinning medication increases the risk of bleeding, be careful while shaving and working with sharp tools. Avoid activities that can cause injuries or open wounds. Use a soft toothbrush, waxed dental floss, and electric razors.
Some people who are taking blood-thinning medication wear medical alert bracelets to let emergency health-care providers know that they are taking anticoagulant medication.
Certain foods interfere with the function of warfarin (Coumadin) in the body. If you are taking warfarin, you’ll need to carefully monitor your diet and keep it consistent from day to day. Foods that can affect warfarin include green leafy vegetables (such as kale, green cabbage, broccoli, and Brussels sprouts), cranberry juice, green tea, mayonnaise, and fish oil. You don’t have to avoid these foods completely; just eat them in small, consistent amounts. Your health-care provider may refer you to a dietician who can help you figure out how to balance your diet with your medication. Be completely honest about your food likes, dislikes, and habits so your health-care provider and dietician can develop an eating plan that works for you.
A blood clot, DVT, or PE can be scary. A PE can be particularly startling because it may occur suddenly, without warning. Talking to friends, family members, and clergy may be helpful. Journaling, or writing your thoughts down in a notebook or on a computer, can also help you process your feelings.
Learning more about your condition can help you feel in control. Ask your health-care provider to explain anything you don’t understand. The more you know about blood clots, risk factors, treatment, and prevention, the better prepared you’ll be to select a treatment and prevention plan that fits your lifestyle.
Date Last Reviewed
Jason Golbin, DO, MS, FCCP
Aleksander Shalshin, MD, MS, FCCP