Medical Disclaimer

Whilst every effort has been made to ensure that the information contained on this site is accurate, it is not a substitute for medical advice or treatment, and Mr A. Abu-Own recommends consultation with a doctor or healthcare professional. The information provided is intended to support patients, not to provide personal medical advice.  Please see our Terms and Conditions for more information.

General Information

Foreword by Mr. Abu-Own

I have a long-standing interest in the prevention and treatment of venous thromboembolism (VTE). This is an area that has undergone major advances in recent years that has revolutionised the way we manage VTE in patients today. An exciting milestone was the introduction of direct oral anticoagulant drugs (DOACs) which allow a fixed dosing regimen without the need for routine coagulation monitoring. This is a useful asset during these times of instability and will no doubt continue to play a role as we plan for the post-COVID era.

This page contains general information for people with a blood clot (thrombus). We discuss what a DVT is, why and how they form, what the complications are and how they can be managed.

I have also included pages on compression stockings and travelling to reflect some frequently asked questions and concerns I encounter from patients.

What is Deep Vein Thrombosis (DVT)?

​DVT is a condition that happens when a blood clot forms in a deep vein, usually in the leg. ​Not to be confused with superficial thrombophlebitis, which affects the superficial veins under the skin. DVTs most commonly start in the calf veins but can extend upwards to the veins in the thigh and pelvis/abdomen. They can also occur in deep veins in other parts of the body such as in the upper arms.

What is Pulmonary Embolism (PE)?

PE is an important and serious complication that can occur in some cases of DVT where part of the blood clot breaks off (embolus) and travels to the lung (pulmonary circulation). One of the main aims of treating a DVT is to prevent this complication from occuring.

What is Venous Thromboembolism (VTE)?

You may also hear this term being used. Because DVT and PE are closely related, VTE is often used as an umbrella term that encompasses both.

Why do DVTs form?

DVTs develop because of three main factors:

  • Reduced flow of blood in the vein
  • Damage to the wall of the vein
  • Changes in consistency of the blood, making it thicker
Because of the effects of gravity during standing, the body attempts to maintain high flow of blood in the leg veins by contracting the calf muscles to squeeze the veins. This helps the flow of blood back to the heart and helps prevent a blood clot from forming in the legs.

Who is at risk of developing a DVT?

DVTs can form in anybody at any time and, at times, for no apparent reason. However, certain circumstances and conditions can increase your risk by affecting one or more of the three factors described above:

  • Immobility: This slows down blood flow in the veins in the legs. The less you move your legs, the less often the calf muscle pump is working to squeeze the veins and maintain blood flow. For instance,
    • Recent surgery results in a significantly increased risk for developing a DVT. In particular, prolonged surgery under general anaesthesia has been shown to be the most common cause for a DVT. This is because your legs are still when you are under anaesthetic and often during the rest period. If surgery is performed in the legs, pelvis or lower abdomen then this increases the risk further. If you are having major surgery, you will usually be given medication with injections and/or tablets to prevent blood clots forming. This is called thromboprophylaxis.
    • An illness or injury causing immobility increases the risk. For example, having a hard plaster cast following a fracture. People admitted to intensive care unit (ICU) are particularly at risk for a number of reasons but partly because they may be kept asleep and immobile by anaesthetic medications.
    • Long distance travel by plane (long haul flight), train or car may cause a slightly increased risk. Following reports in the press of occasional deaths due to fatal pulmonary embolisms, it has become common for patients to express concern about the risks of DVT during long haul flights. Despite this, the risk for most people is very small.
  • Damage/injury to the deep veins. This can increase the chance of a DVT. For example,
    • A Previous DVT can damage the lining of the deep veins​. So if you have had one before then you are at increased risk of having another one.
    • Injury caused by a needle, for example, treatment with a drip in hospital where a tube is inserted into a vein to give fluids. Drug users who inject into their veins are also at increased risk, particularly if they inject illicit drugs into their legs or groin.​​
    • Injury by trauma or surgery (e.g. Hip or Knee surgery).
  • Age. Older people are more likely to develop DVT as blood tends to get thicker as you age. They are more likely to have other health problems that predispose them to DVT and are more likely to have mobility problems.
  • Cancer and its treatments (e.g chemotherapy). Cancer patients often have thicker blood and may be less mobile. Sometimes a DVT happens in a person who has not yet been diagnosed with cancer. Investigations looking for the cause may show cancer to be the underlying cause.
  • Severe heart disease. If your heart struggles to pump blood around the body, the reduced blood flow gives blood more of a chance to form a clot.
  • Pregnancy. Pregnant women are at least 5 times more likely to develop a DVT than non-pregnant women. The highest risk being just after giving birth and an increased risk remains for up to 6 weeks after birth. The level of blood-clotting proteins increases during pregnancy, while anticlotting protein levels decrease. The enlarged womb can also compress the main veins in the pelvis bringing blood back to the heart from the legs, reducing the blood flow in the legs.
  • Contraceptives and Hormone Replacement Therapy (HRT) containing oestrogen give a slightly increased risk.
  • Family history of DVT. Having a close relative who has had one increases your risk.
  • Thrombophilia: this terms refers to a group of conditions that cause blood to clot more easily in the body than usual. There are many types of thrombophilia. Some run in families (inherited) and others are acquired. Common types include:
    • factor V Leiden
    • protein C deficiency
    • protein S deficiency
    • antithrombin deficiency
    • antiphospholipid syndrome
  • Obesity: If your BMI is more than 30 your risk is increased. The risk increases with increasing size.
  • Dehydration. This makes the blood thicker and more liable to clot.

​​What are the symptoms of a DVT?

DVTs most commonly start to develop below the knee in the calf. 50% of DVTs produce no symptoms at all and a DVT is only diagnosed if a complication such as pulmonary embolism occurs. Symptoms you may experience include:

  • Pain and tenderness in the calf
  • Swelling of the calf (extending to the thigh in 'iliofemoral DVT')
  • Hotness and redness of the calf.

What are the symptoms of a PE?

The symptoms vary. A small PE may not cause any symptoms. A medium sized PE can cause breathing problems (sudden or gradual in onset) and chest pain (worse on breathing in). A large PE can cause collape and sudden death. The symptoms of DVT may also be present (e.g. painful swollen calf).

Are there any other complications besides PE?

Some people who develop DVT later go on to develop long term symptoms in the calf - this is called Post Thrombotic Syndrome (PTS). PTS is thought to develop because the blockage from the blood clot causes engorgement of blood in the smaller blood vessels in the lower leg, leading to increased venous pressure (venous hypertension) in these veins. Over time, this increased pressure exerts an effect on the soft tissue of the calf. Symptoms can range from mild to severe and include calf pain, discomfort, swelling and venous eczema. The combination of discolouration and hard skin in the lower leg above the ankle (gaiter area) is called Lipodermatosclerosis (a sign of chronic venous insufficiency). A venous ulcer on the skin of the lower leg may develop in severe cases. PTS & venous leg ulcer (the ultimate venous disease) are more likely to occur if the DVT affects the bigger veins in the thigh and pelvis (Iliofemoral DVT). It is also more common in people who are overweight and in those who have had more than one DVT in the same leg.

What tests are used to diagnose DVT?

It can be difficult for your doctor to be sure whether you have had a DVT just from the symptoms as there are many causes of a painful, swollen calf. You will normally be advised to have some urgent tests to confirm or rule out the diagnosis. The two commonly used tests are:

  • D-Dimer: This detects the fragments from the breakdown products of a blood clot. Unfortunately, this test can be positive in other conditions and therefore does not confirm a DVT on its own. It is useful for being able to exclude a DVT i.e. if the test is negative then a DVT is unlikely.
  • Duplex Ultrasound scan: This is a simple, non-invasive test that can be used to assess the blood flow in the leg veins and if there is a thrombus.
Other tests occasionally needed include CT and MR Venography. Conventional contrast venography is rarely necessary or justified in modern practice.

What are the aims of treatment for DVT?

  1. To prevent a pulmonary embolism
  2. To reduce the risk of post thrombotic syndrome
  3. To reduce the risk of a venous ulcer
  4. To reduce the risk of having another DVT in the future.

What are the treatments options for DVT?

1. Anticoagulants The main treatment for DVT is with anticoagulant medications ('blood thinners'). Blood thinning as a term is somehwhat misleading because they do not actually thin the blood, but they alter certain chemicals in the blood to stop clots forming easily. They also do not breakdown the clot but prevent existing clots from getting bigger (extending) to allow the bodies own mechanism to break up the clot. If you have a DVT, you will usually need an anticoagulant medicine for at least three months. This may be longer for some people and varies from person to person. For certain patients, anticoagulant therapy may be required life-long. Your doctor or anticoagulant clinic will advise you how long your treatment should be for. A serious pulmonary embolus is rare if you start anticoagulation treatment early after a DVT. The tablets used may take a few days to start working properly, so normally you have some fast-acting injections given for the first few days until the tablets are working properly. Pregnant women will need to be exclusively on injections (heparin) for the duration of their treatment. The injections used are usually given just under the skin (subcutaneously). These include:

  • Heparin (low molecular weight Heparin, or LMWH) - including enoxaparin, dalteparin, tinzaparin and others.
  • Fondaparinux
Once a DVT has been confirmed you will also be started on an anticoagulant tablet. There are two main options:
  • Warfarin.
    • This has been the main anticoagulant for many years. The aim is to get the dose high enough so that blood will not clot easily, but not too high that it causes bleeding problems. This is why those on warfarin require regular blood clotting tests (INR) to check that their blood clotting ability is at an appropriate level. These tests will be frequent at first but less frequen once you are stabilised on the right dose.
    • We usually aim for an INR of between 2-3 for those taking warfarin to treat a DVT.
    • If you are pregnant, you should not take warfarin as it can potentially cause harm (birth defects) to the unborn child.
  • Direct oral anticoagulant (DOAC) drugs e.g. rivaroxaban and apixaban.
    • These are commonly used for the prevention and treatment of VTE. There has been no debate within the clinical community that these are safe and effective, but they are more expensive than warfarin. DOACs are increasingly used to replace warfarin for anticoagulation.
    • A big advantage of these medications is that they do not need regular INR tests to monitor your clotting level like with warfarin.
    • A disadvantage is that there is no effective antidote (like with warfarin) to stop you bleeding too easily (some that produce partial reversal are becoming available).
    • The DOAC dose to be used is standard for most patients, except for certain situations e.g. impaired kidney function where the dose is reduced. For this reason, a simple blood test looking at the kidneys function is required before starting a DOAC.
    • Once the dose has been determined you can be assured that that your fixed daily dose will achieve adequate and consistent anticoagulation. The dose of a DOAC used to prevent DVT (prophylaxis) is different (less, usually half) than the dose used to treat an established DVT.
    • These tablets are not suitable for everyone and are not used in those who needed an INR of more than 3 while on warfarin, those with poor renal function, pregnant and breast feeding women and those with antiphospholipid syndrome.
2. Compression Stockings Most people who develop a DVT will be advised to wear compression stockings. Other names for this include compression hosiery or thrombo-embolic deterrent stockings (TED stockings). Stockings reduce leg swelling, decrease the risk of getting another DVT and of getting post-thrombotic syndrome (long term calf changes). Before you start wearing compression stockings, it is important that you have a Doppler test to ensure the circulation in the arteries of your legs is satisfactory. Following a DVT, you should wear these every day for at least 2 years. People often do not like wearing them because they find them uncomfortable, or difficult to put on, or because they don't look very nice. But they do help reduce leg swelling after DVT in the short term and reduce the likelihood of long term complications such as PTS and venous ulcers. For more information, visit our Medical Stockings page. 3. Regular walks and leg raising Unless your doctor advises against this, you should walk regularly after you are discharged from hospital. Walking will improve the circulation in the affected leg and reduce the chance of getting another DVT. When resting you should raise your leg so that your foot is higher than your hip. This allows you to utilise gravity to help reduce the pressure in the calf veins and prevent blood from pooling in the legs. Sitting on a sofa with your feet on a footstool is not adequate as your feet are still below your hips in this position. Try reclining on a sofa with your leg up on a cushion. When sleeping, raise the foot of the bed a few inches if it is comfortable to sleep like this. 4. Other treatments In selected cases, other treatments may be considered. These include:
  • Thrombolysis. Thrombolytic drugs such as Tissue Plasminogen Activator (TPA) work by dissolving already formed clots. They may be given directly into the vein but are now usually given directly into the clot by a tube (catheter-directed thrombolysis). Research suggests that this treatment results in fewer people developing post-thrombotic syndrome but it is unclear whether it reduces the risk of a PE or of another DVT.
  • Thrombectomy. This is an operation where the surgeon directly removes the blood clot from the leg vein (in DVT) or pulmonary artery (in PE). This is rarely used and reserved for exceptional circumstances.
  • IVC filter. This is a procedure where a filter is placed in a large vein to the heart called the inferior vena cava (IVC). The aim is to stop any blood clots that have formed in the leg or abdomen from reaching the heart and therefore the lungs (PE). This may be considered if anticoagulation cannot be used or if it fails to prevent PEs.

How do I prevent a DVT?

For many people, a DVT occurs as a one-off event following a major operation. For these people, once they have completed their full course of treatment there isn't usually much else they need to do. Your doctor will advise you about this. If they identify you as having a long term risk for future (recurrent) DVTs, you may need to take your anticoagulant medicine longer term. Other measures that may help prevent first or recurrent DVTs include:

  • Avoiding long periods of immobility, such as sitting in a chair.
  • If you are having a major operation (particularly in the hip area or legs), there are many preventative measures to reduce the risk:
    • Anticoagulation just before the operation (thromboprophylaxis). Commonly heparins such as enoxaparin. Fondaparinux is also given in some circumstances. Newer anticoagulant tablets (DOACs) can be used as thromboprophylaxis in hip or knee replacement surgery.
    • An inflatable sleeve connected to a pump is used to compress the legs during an operation
    • You may be given compression stockings to wear whilst in hospital
    • Patients should get up and be active as early as possible after an operation, if possible.
  • Being in hospital without having an operation is also recognised as a significant risk for having a DVT. For this reason:
    • When admitted to hospital, everyone has their risk of blood clots checked​. This is called a VTE risk assessment and is mandatory following admission to hospital.
    • The results of the risk check are used to decide whether further preventative measures are required e.g. anticoagulants and stockings.
    • Your healthcare team will explain if you are to continue on a preventative drug (thromboprophylaxis) after leaving hospital, because in some cases, a DVT can develop after discharge from hospital.
  • For long flights, train or coach journeys you should walk up and down the aisle every now and then, if possible. While travelling, you can also exercise your calf muscles whilst sitting in your seat. Stay hydrated and avoid alcohol and sleeping medications. If you have had a previous DVT, please see your doctor for advice before you travel long journeys. For more information, visit our Advice For Travellers page.
  • People who are overweight would benefit from losing weight to reduce their risk.