Venous Thrombosis

Venous thrombosis is a condition where blood clots form inside your veins, blocking blood flow and potentially causing serious health problems. While these clots most commonly develop in the legs, they can occur anywhere in the body and sometimes travel to the lungs, creating a life-threatening emergency.

Table of contents

• What is venous thrombosis?
• Types of venous thrombosis
• How blood clots form
• Signs and symptoms
• Risk factors
• Diagnosis
• Complications
• Treatment
• Prevention
• Living with venous thrombosis

What is venous thrombosis?

Venous thrombosis happens when a blood clot, called a thrombus, forms inside a vein and blocks or restricts blood flow^[1]. The term “thrombo” means blood clot, “embolism” means a circulating particle that causes an obstruction, and “venous” means in the veins^[2]. While blood clotting is a normal and healthy response to a cut or wound, sometimes clots form when there was no injury, or they don’t dissolve after healing is complete^[2].

Veins carry blood from the extremities of your body back to your heart. When a vein becomes blocked by a clot, blood pools behind the blockage, causing inflammation. Cells ahead of the blockage can’t get the oxygen and nutrients they need, which can cause serious damage to veins, tissues, and organs^[2].

As many as 600,000 venous thrombosis events occur each year in the United States^[1]. In fact, approximately 1 to 3 in every 1,000 adults develop this condition annually in the United States, and up to 300,000 people die each year as a result^[13]. It’s the third most common vascular disease, behind heart attacks and strokes^[13].

Types of venous thrombosis

The term venous thromboembolism (VTE) refers to blood clots that occur in the veins. VTE includes two main types: deep vein thrombosis and pulmonary embolism^[4].

Deep vein thrombosis (DVT)

Deep vein thrombosis occurs when a blood clot forms in a deep vein, usually in the lower leg, thigh, or pelvis^[1]. These are veins located deep within your body, embedded in the muscles of your legs or arms^[2]. DVT can also occur in other parts of your body, including your arm, brain, intestines, liver, or kidney^[13]. DVTs can also develop in the arms, especially if there is a large intravenous central line in the vein^[1].

Pulmonary embolism (PE)

A pulmonary embolism occurs when a blood clot breaks loose and travels through the bloodstream to the lungs^[1]. When a piece of thrombus breaks off and is transported through the bloodstream, it becomes an embolus^[7]. If this traveling clot lodges in the blood vessels of your lungs, it becomes a pulmonary embolism, which can be life-threatening^[2].

Superficial venous thrombosis

Superficial venous thrombosis, also called phlebitis or superficial thrombophlebitis, is when blood clots develop in a vein close to the surface of your skin^[13]. These types of blood clots rarely travel to your lungs unless they move from the superficial system into the deep venous system first^[13].

How blood clots form

Blood clotting is a normal and healthy response to a superficial cut or wound. Your blood coagulates—partially solidifies—to keep it from leaking too fast from a hole. Blood clotting can also be triggered by an infection, which irritates the lining of the blood vessel like a wound^[2].

When the wound or infection begins to heal, the clot is supposed to dissolve. But sometimes it doesn’t. And sometimes blood clots form when there was no wound at all^[2]. Blood clots can happen for many reasons, but generally they develop because of injury to a vein, slow blood flow caused by limited movement, certain chronic medical illnesses, or increased levels of certain hormones^[4].

Sometimes blood clots can happen for reasons that are never identified. These are called “unprovoked” or unexplained blood clots^[11].

Signs and symptoms

Symptoms of deep vein thrombosis

About half of people with DVT have no symptoms at all^[4]. Up to 30% of people with a DVT don’t have symptoms, but sometimes the symptoms are very mild and may not raise concern^[13]. When symptoms do occur, they include^[1][3][6]:

• Swelling in the affected leg or arm, sometimes happening suddenly
• Pain or tenderness in the leg or arm, often starting in the calf and may only occur when standing or walking
• A feeling of warmth in the affected area
• Redness or skin discoloration—the skin may appear red or purple, depending on your natural skin color
• Visible veins near the skin’s surface that may be larger than normal
• Throbbing pain in one leg when walking or standing up

If blood clots affect veins deep inside your abdomen, you may experience abdominal pain or flank pain. If they affect veins in your head, you may have a severe headache^[13].

Symptoms of pulmonary embolism

You can have a PE without any symptoms of a DVT^[4]. The warning signs and symptoms of a pulmonary embolism include^[1][4]:

• Sudden shortness of breath or difficulty breathing
• Chest pain or discomfort that usually worsens with a deep breath or coughing
• Faster than normal or irregular heartbeat
• Coughing or coughing up blood
• Very low blood pressure, lightheadedness, or fainting

If you have any of these signs or symptoms, you should seek medical help immediately^[4]. If you develop symptoms of a pulmonary embolism—a life-threatening complication of deep vein thrombosis—seek emergency medical help by calling emergency services right away^[3].

Risk factors

Almost anyone can have a DVT or PE. However, certain factors can increase the chance of having this condition^[4]. The risk of developing venous thrombosis is highest after major surgery, major injury, or during periods of infection and inflammation. This is because blood clots can develop in veins damaged by surgery or injury. Lack of movement after surgery or while traveling long distances can raise the likelihood of blood clotting. Inflammation and serious infection also raise the likelihood of blood clots^[1].

Factors that increase the risk of developing venous thrombosis include^[4][6][9]:

• Age—people over 60 are at higher risk
• Recent surgery, especially major operations
• Long periods of inactivity, such as being confined to bed or sitting during long flights or car rides (more than 3 hours)
• Pregnancy and the postpartum period (up to 6-8 weeks after delivery)
• Taking hormones, especially for birth control or hormone replacement therapy
• All types of cancer
• Obesity or being overweight
• Smoking or tobacco use
• Chronic medical illnesses such as heart failure
• Chronic inflammatory diseases
• Family history of blood clots
• Previous DVT or PE
• Varicose veins
• Genetic predispositions that cause the blood to clot more easily, such as thrombophilia
• COVID-19 infection
• Dehydration

More than half of all DVTs happen as a result of being in the hospital from a medical illness or following surgery. The reason DVTs are more common after a hospital stay is because you’re lying in bed most of the time instead of moving around like you normally would^[13].

Diagnosis

If you have recently had surgery or have other risk factors of venous thrombosis, talk to your healthcare provider about your risk and how to prevent blood clots^[1]. If you think you have DVT, you should be referred to hospital within 24 hours for an ultrasound scan^[6].

To diagnose DVT, your healthcare provider will do a physical exam and ask questions about your symptoms. The provider will check the legs for swelling, tenderness, or changes in skin color^[10].

Blood tests

Venous thrombosis is suspected when the patient presents symptoms combined with an elevated level of D-dimer in the blood, which indicates a blood clotting condition^[9]. D-dimer is a type of protein produced by blood clots. Almost all people with severe DVT have increased blood levels of D-dimer. This test often can help rule out pulmonary embolism^[10].

Imaging tests

The diagnosis is confirmed with a venous Doppler ultrasound test^[9]. This noninvasive test uses sound waves to create pictures of how blood flows through the veins. It’s the standard test for diagnosing DVT. For the test, a healthcare provider gently moves a small hand-held device (transducer) on the skin over the body area being studied. Additional ultrasounds may be done over several days to check for new blood clots or to see if an existing one is growing^[10].

You may also have an X-ray of the vein called a venogram. For this test, you’ll be injected with a dye to show where the blood clot is^[6]. Other imaging tests such as magnetic resonance imaging (MRI) scans may be done to diagnose DVT in veins of the abdomen^[10].

Complications

Pulmonary embolism

The most serious complication of DVT happens when a part of the clot breaks off and travels through the bloodstream to the lungs, causing a blockage called pulmonary embolism^[4]. A pulmonary embolism restricts oxygen and blood flow to your lungs while increasing blood pressure in your arteries. This causes pulmonary hypertension, which in turn can cause heart failure and death^[2].

If the clot is small and with appropriate treatment, people can recover from PE. However, there could be some damage to the lungs. Chronic thromboembolic pulmonary hypertension is a complication that can happen after a PE with a large clot. It can stop blood from reaching the lungs and can be fatal^[4].

Post-thrombotic syndrome

As many as half of those who get a DVT in their legs develop symptoms of intermittent leg pain and swelling that may last months to years. These symptoms are called post-thrombotic syndrome (PTS) and can happen because of damage to the valves and inner lining of your veins, leading to blood “pooling” more than it should. This increases the pressure inside your veins and causes pain and swelling^[13].

One-third to one-half of people who have a DVT will have this long-term complication. Characteristics of this condition include pooling of blood, chronic leg swelling, increased pressure within your veins, increased skin pigmentation or discoloration, and in severe cases, leg ulcers known as venous stasis ulcers^[4][13].

The risk of developing post-thrombotic syndrome is reduced if the patient begins treatment quickly and receives appropriate follow-up care^[9].

Treatment

The primary objectives for the treatment of deep venous thrombosis are to prevent pulmonary embolism, reduce morbidity, and prevent or minimize the risk of developing post-thrombotic syndrome^[12]. Not everyone who is diagnosed with venous thrombosis needs treatment. If the blood clot needs treatment, your provider will likely prescribe medicine first^[14].

Blood thinners (anticoagulants)

Blood thinners, also called anticoagulants, are the mainstay of medical therapy for venous thrombosis. These medicines keep blood clots from getting larger and stop new clots from forming^[1][14]. Blood thinners reduce the risk of developing more clots^[10].

Conventional blood thinners include warfarin and heparin, but newer blood-thinning medicines called direct oral anticoagulants (DOACs) are also available. Your provider will work with you to determine which medicine is best for you based on your medical history^[14].

Depending on the blood thinner, you may be given an injection (shot), take a pill, or have an intravenous tube (IV) inserted. You may need to take blood thinners for several months or for a lifetime. The specific amount of time depends on many factors, like the type of blood thinner and the cause of the blood clot^[14].

Possible side effects of blood thinners include bleeding, especially if you are taking other medicines such as aspirin that also thin your blood^[14]. If you take warfarin, you’ll need to watch what you eat. Vitamin K can affect how the drug works, so you have to be careful about the amounts of kale, spinach, Brussels sprouts, chard, or collard or mustard greens you eat. Green tea, cranberry juice, and alcohol can also affect blood thinners^[23].

Medicines to dissolve blood clots

Medicines called thrombolytics are used to dissolve blood clots. These medicines are used for large blood clots that cause severe symptoms or other serious complications. Because thrombolytics can cause sudden bleeding, they are used only for serious and potentially life-threatening events, such as pulmonary embolism. You will get this medicine through an IV^[14].

Surgical and catheter-based procedures

In some cases, including emergencies, your provider may need to do a catheter-assisted blood clot removal^[14]. You may need a surgical procedure if you cannot take blood-thinning medicine^[14].

Some patients may need a filter inserted into the large vein that leads from the legs to the heart, to block any future clots from reaching the lungs^[5].

Compression therapy

Your provider might also recommend compression stockings. These special tight-fitting socks keep a certain amount of pressure on your leg, and that can help with blood flow after a DVT. Your doctor might also recommend them after a PE to boost your circulation^[23].

Prevention

If you are preparing to go to the hospital for a procedure or have other risk factors, talk with your healthcare provider about a plan for preventing blood clots from forming^[17].

After surgery

The chance of developing venous thrombosis is highest in the first 3 months after surgery and lowers with time. Your provider may give you suggestions to help prevent blood clots^[17]:

• Keep moving—helping your blood circulate makes it harder for clots to form. Your provider may tell you to move around as soon as possible after surgery and as you heal. If you cannot get up and walk, try to flex and stretch your feet to improve blood flow in your calves
• Apply pressure—gentle pressure keeps blood from pooling and clotting. Your provider may talk to you about applying pressure, for example, by wearing a sleeve or boot that periodically fills with air or by wearing compression stockings
• Take blood thinner medicines—sometimes preventive therapy starts before surgery, or your provider may prescribe a blood thinner to take during your recovery period^[17]

General prevention tips

There are things you can do to lower your chance of getting venous thrombosis^[6][16][18]:

• Stay active—regular exercise helps improve blood circulation. Aim for at least 30 minutes of moderate exercise daily. Activities like walking, cycling, and swimming are excellent options
• Maintain a healthy weight—being overweight increases pressure on your veins. Adopting a balanced diet and maintaining a healthy weight can reduce your risk
• Stay hydrated—drinking plenty of water prevents blood from thickening, reducing clot formation. Dehydration makes DVT more likely
• Don’t sit still for long periods—get up and move around every hour or so. If you have a sedentary job, make sure to take breaks. Avoid sitting for more than 2 hours at a time
• Don’t cross your legs while sitting—that position can affect your circulation
• Quit smoking—smoking damages blood vessels, increasing the risk of clot formation
• Don’t drink lots of alcohol

Travel precautions

If you’re traveling for 3 hours or more by plane, train, or car, there are things you can do during the journey to lower your chances of getting blood clots^[6][16]:

• Wear loose clothing
• Drink plenty of water
• Avoid alcohol
• Walk around when possible—on a plane, try to move around the cabin once an hour
• While seated, flex your ankles to keep blood flowing. Deep knee bends can help get your circulation going

Living with venous thrombosis

Life after deep vein thrombosis or pulmonary embolism can be stressful. Recovery can take upwards of several months, and you’ll need to make sure you adhere to your doctor’s medication and treatment schedule^[16].

After the initial recovery, you’ll also need to take precautions to prevent future blood clots. This is especially important because a history of DVT may increase your risk of another blood clot^[16]. If you’ve had a blood clot before—whether in your leg, arm, or lungs—your chances of another one are higher^[23].

Individual risk will depend on the cause of the blood clot. For patients whose DVT is the result of a temporary risk factor, such as surgery or trauma, the risk of future blood clots is quite low. For those whose DVT occurred without any obvious cause, if they’ve been treated with a blood thinner for three to six months, the risk of having a recurrent blood clot in the next year is about 10 to 15 percent^[16].

Follow-up care

After you leave hospital, you’ll be encouraged to walk regularly, keep your affected leg raised when you’re sitting, and delay any flights or long journeys until at least 2 weeks after you start taking blood-thinning medicine^[6].

You may need to wear compression stockings for two years^[13]. It’s sometimes normal for the affected limb to stay slightly swollen after treatment. After a clot in your lungs, you might feel mild pain or pressure in your chest^[23].

Warning signs to watch for

Watch out for new or worse pain, pressure, or cramping in your calf—that could signal a new DVT. Shortness of breath or fainting could be signs of another PE. If you have any of these, call emergency services and get medical care right away^[23].

Let all your doctors know if you’ve had a blood clot of any kind. And if you take blood thinners, tell your dentist when you make your appointment^[23].

Safety precautions

If you take blood thinners, you may be more likely to bleed from small injuries, so it’s important to be careful when trimming your nails. You should wear gloves when you use sharp tools, and wear safety gear for sports and hobbies^[23].

Tell all your healthcare providers about any other medicines you take. Some antibiotics can keep blood thinners from working the way they should. You should be careful with over-the-counter herbal supplements—a few, including ginseng, flaxseed, and fish oil, can affect how blood thinners work^[23].