Deep vein thrombosis (DVT)

The typical signs of deep vein thrombosis include:

• Pain in a leg or hip
• Tenderness
• Swelling and a tight feeling
• Warm, reddish skin
• Muscle cramps

The symptoms usually only occur in one leg because thrombosis typically only develops on one side of the body.

The symptoms also depend on where the clot is blocking the vein: near the calf, behind the knee, or in the thigh or pelvis. Thrombosis below the knee usually only causes symptoms in the lower leg. Thrombosis that is higher up or more extensive can also lead to symptoms in the thigh or pelvis.

Blood clots may form if the blood flow in a vein is too slow, if the blood clots too easily or if the wall of a blood vessel is damaged. That may result from:

• Longer periods of bed rest, for instance in the hospital, after a bone fracture or injury. Spending a lot of time in bed and not moving much can lead to a build-up of blood in a leg.
• Blood clotting disorders: Some people are born with a disease that makes their blood clot too much.
• Major surgery: Major surgical procedures and serious injuries cause damage to blood vessels. The body then increases your blood's clotting ability to stop the bleeding and close wounds. This involves the release of more coagulation factors (clotting factors).

There are also various other things that can increase someone's risk of developing thrombosis:

• Previous thrombosis
• Being older than 60 years
• Family history (parents or siblings had thrombosis)
• Certain types of cancer
• Heart failure
• Being severely overweight (obese)
• Taking the contraceptive pill
• Hormone therapy for menopause
• Very noticeable varicose veins
• Smoking
• Certain inflammatory diseases
• Pregnancy
• Regular long-haul journeys where you spend a lot of time sitting

Taken on their own, though, most of these risk factors only slightly increase the risk of DVT.

One common complication of DVT is known as post-thrombotic syndrome (PTS). This condition develops if the DVT has damaged the walls or valves of a vein, causing the blood to constantly build up in the vein. It often occurs a few weeks or months after thrombosis.

People with PTS may have a swollen leg that feels heavy and hurts. The skin on their leg may also become discolored and itch, and a rash may develop. More severe cases of post-thrombotic syndrome can lead to chronic wounds. It's important to seek medical advice quickly if you have these symptoms.

A rarer but more serious complication of deep vein thrombosis is known as pulmonary embolism. This happens if the blood clot breaks away from its original site and is carried through the blood stream to the lungs, where it blocks a blood vessel. The symptoms of pulmonary embolism include:

• Sudden shortness of breath
• Chest pain (particularly when breathing in or coughing)
• Dizziness, lightheadedness or unconsciousness
• Rapid heartbeat
• Coughing up blood (rare)

Pulmonary embolism needs to be treated quickly because the blocked blood vessel causes blood to build up between the heart and lungs. This can put too much strain on the heart and eventually lead to life-threatening heart failure.

If pulmonary embolism develops, then it usually does so within two weeks of the DVT developing. The risk of pulmonary embolism is greater if the thrombosis is in the upper part of your leg or in your pelvis than if you have thrombosis in your lower leg. This is also true for thrombosis that causes very noticeable symptoms.

Deep vein thrombosis can’t be diagnosed for sure based on typical symptoms alone. Symptoms such as pain, swelling and red skin can be caused by other things too, including an inflammation of superficial veins, varicose veins, erysipelas or narrow leg arteries (peripheral artery disease, or PAD).

To diagnose DVT, a blood test called a D-dimer test is usually done first. This test reacts to substances that are released when blood clots are broken down. The substances are called D-dimers. If the results of the test are normal, doctors can be quite sure that you don’t have DVT. If the results are abnormal, a special kind of ultrasound scan (a Doppler ultrasound) is done in order to confirm the diagnosis. Doppler ultrasounds provide information about the condition of the deep veins in the legs and blood flow in the veins.

If there’s good reason to believe that someone has a DVT from the start, an ultrasound scan is usually done immediately.

An x-ray of the blood vessels (angiography) is only rarely necessary. Angiography involves using a catheter to inject a contrast agent (a dye-like substance) into the vein so that doctors can see where the blood vessels are narrowed.

There are different ways to try to prevent DVT. People who are recovering from surgery or an injury usually need to spend a few days resting in bed. But it's still important to move if you can and to get up again as soon as possible. Small exercises like wiggling your toes are recommended to help with blood circulation.

Medications called anticoagulants can be used for a few days or weeks to help reduce blood clotting. Their suitability will depend on things like whether you have had surgery, how major it was and whether you have risk factors for thrombosis. These medications can be injected or swallowed.

Compression stockings can also be used. The stockings put pressure on the veins, which helps the blood to flow. If you're already using anticoagulants, you don't need to use compression stockings. But they are an option for people who can't use anticoagulants. That is rare, though.

Deep vein thrombosis is usually treated for a few days in the hospital, but it can also be treated in an outpatient setting. This involves using the same medications that are used to prevent thrombosis.

To make sure that the blood clot dissolves completely, patients are advised to take anticoagulant (anti-clotting) tablets for three to six months after having the acute treatment. Sometimes it’s a good idea to take them for even longer too. It's important to take anticoagulants as prescribed. That helps to prevent both another thrombosis and post-thrombotic syndrome.

To lower the risk of post-thrombotic syndrome, people are sometimes advised to wear compression stockings for up to two years. Studies on their effectiveness haven't shown any clear results, though. So it's best to talk with your doctor about whether preventive treatment with compression stockings is a good idea for you.

Some people aren't able to use anticoagulants – for example, because they tend to bleed more. Then a catheter can be used to implant a small metal filter (inferior vena cava filter, or IVC filter) into the large vein above the kidneys. The filter is meant to catch any blood clots that could otherwise travel from the leg to the lungs and cause a pulmonary embolism. There is not enough research on the pros and cons of IVC filters. They are only used in exceptional cases – partly due to the possible risks. Some medical societies even advise against using them.