Deep Vein Thrombosis and Venous Thromboembolism

Venous thromboembolism (VTE) is a common and potentially fatal condition. It involves blood clots (thrombi) developing in the circulation. This usually occurs secondary to stagnation of blood and hyper-coagulable states. When a thrombus develops in the venous circulation, it is called a deep vein thrombosis (DVT). 

Once a thrombus has developed, it can travel (embolise) from the deep veins, through the right side of the heart and into the lungs, where it becomes lodged in the pulmonary arteries. This blocks blood flow to areas of the lungs and is called a pulmonary embolism (PE).

If the patient has a hole in their heart (for example, an atrial septal defect), the blood clot can pass through to the left side of the heart and into the systemic circulation. If it travels to the brain, it can cause a large stroke.


Risk Factors

There are several factors that can put patients at higher risk of developing a DVT or PE. In many of these situations (e.g., surgery), we give patients prophylactic treatment to prevent VTE.

  • Immobility
  • Recent surgery
  • Long haul travel
  • Pregnancy
  • Hormone therapy with oestrogen (combined oral contraceptive pill and hormone replacement therapy)
  • Malignancy
  • Polycythaemia
  • Systemic lupus erythematosus
  • Thrombophilia


TOM TIP: In your exams, when a patient presents with possible features of a DVT or PE, ask about risk factors such as periods of immobility, surgery and long haul flights to score extra points.



Thrombophilias are conditions that predispose patients to develop blood clots. There are a large number of these:

  • Antiphospholipid syndrome
  • Factor V Leiden 
  • Antithrombin deficiency
  • Protein C or S deficiency
  • Hyperhomocysteinaemia
  • Prothombin gene variant
  • Activated protein C resistance


TOM TIP: If you remember one cause of recurrent venous thromboembolism, remember antiphospholipid syndrome. The common association you may come across in exams is recurrent miscarriage. The diagnosis can be made with a blood test for antiphospholipid antibodies.


VTE Prophylaxis

Every patient admitted to hospital should be assessed for their risk of venous thromboembolism (VTE). If they are at increased risk of VTE, they should receive prophylaxis unless contraindicated. Prophylaxis is usually with low molecular weight heparin, such as enoxaparin. Contraindications include active bleeding or existing anticoagulation with warfarin or a DOAC. 

Anti-embolic compression stockings are also used, unless contraindicated. The main contraindication for compression stockings is significant peripheral arterial disease.


DVT Presentation

DVTs are almost always unilateral. Bilateral DVT is rare and bilateral symptoms are more likely due to an alternative diagnosis such as chronic venous insufficiency or heart failure. DVTs can present with:

  • Calf or leg swelling
  • Dilated superficial veins
  • Tenderness to the calf (particularly over the site of the deep veins)
  • Oedema
  • Colour changes to the leg

To examine for leg swelling, measure the circumference of the calf 10cm below the tibial tuberosityMore than 3cm difference between calves is significant.

Always ask questions and examine with the suspicion of a potential pulmonary embolism as well.


Wells Score

The Wells score predicts the risk of a patient presenting with symptoms having a DVT or PE. It includes risk factors such as recent surgery and clinical findings such as unilateral calf swelling 3cm greater than the other leg.



D-dimer is a sensitive (95%), but not specific, blood test for VTE. This makes it helpful in excluding VTE where there is a low suspicion. It is almost always raised if there is a DVT; however other conditions can also cause a raised d-dimer:

  • Pneumonia
  • Malignancy
  • Heart failure
  • Surgery
  • Pregnancy


Doppler ultrasound of the leg is required to diagnose deep vein thrombosis. NICE recommends repeating negative ultrasound scans after 6-8 days if a positive D-dimer and the Wells score suggest a DVT is likely.

Pulmonary embolism can be diagnosed with a CT pulmonary angiogram (CTPA) or ventilation-perfusion (VQscan. CTPA is usually preferred, unless the patient has significant kidney impairment or a contrast allergy.


Initial Management

The initial management for a suspected or confirmed DVT or PE is with anticoagulation. In most patients, NICE (2020) recommend treatment dose apixaban or rivaroxaban. It should be started immediately in patients where DVT or PE is suspected, and there is a delay in getting the scan.

The NICE guidelines (2020) recommend considering catheter-directed thrombolysis in patients with a symptomatic iliofemoral DVT and symptoms lasting less than 14 days. This involves inserting a catheter under x-ray guidance through the venous system to apply thrombolysis directly into the clot.


Long Term Anticoagulation

The options for long term anticoagulation in VTE are a DOACwarfarin, or LMWH.

DOACs are oral anticoagulants that do not require monitoring. They were called “novel oral anticoagulants” (NOACs), but this has been changed to “direct-acting oral anticoagulants” (DOACs). Options are apixabanrivaroxabanedoxaban and dabigatran. They are suitable for most patients, including patients with cancer.

Warfarin is a vitamin K antagonist. The target INR for warfarin is between 2 and 3 when treating DVTs and PEs. It is the first-line in patients with antiphospholipid syndrome (who also require initial concurrent treatment with LMWH).

Low molecular weight heparin (LMWH) is the first-line anticoagulant in pregnancy.

Continue anticoagulation for:

  • 3 months if there is a reversible cause (then review)
  • Beyond 3 months if the cause is unclear, there is recurrent VTE, or there is an irreversible underlying cause such as thrombophilia (often 6 months in practice)
  • 3-6 months in active cancer (then review)


Inferior Vena Cava Filter

Inferior vena cava filters are devices inserted into the inferior vena cava, designed to filter the blood and catch any blood clots travelling from the venous system, towards the heart and lungs. They act as a sieve, allowing blood to flow through whilst stopping larger blood clots. They are used in unusual cases of patients with recurrent PEs or those that are unsuitable for anticoagulation.


Investigating Unprovoked DVT

When patients have their first VTE without a clear cause, the NICE guidelines from 2020 recommend reviewing the medical history, baseline blood results and physical examination for evidence of cancer. The previous 2012 guidelines recommended routinely considering investigations such as a chest x-ray and CT abdomen-pelvis, although this is no longer recommended.

In patients with an unprovoked DVT or PE that are not going to continue anticoagulation (they have finished 3-6 months of treatment and are due to stop), NICE recommends considering testing for:

  • Antiphospholipid syndrome (check antiphospholipid antibodies)
  • Hereditary thrombophilias (only if they have a first-degree relative also affected by a DVT or PE)


Budd-Chiari Syndrome

Budd-Chiari syndrome is where a blood clot (thrombosis) develops in the hepatic vein, blocking the outflow of blood. It is associated with hyper-coagulable states. It causes acute hepatitis.

It presents with a classic triad of:

  • Abdominal pain
  • Hepatomegaly
  • Ascites


Management involves anticoagulation (heparin or warfarin), investigating for the underlying cause of hyper-coagulation and treating hepatitis.


Last updated February 2022