What is deep vein thrombosis (DVT)?

Legs have two sets of veins—superficial veins and the deep veins that drain blood from the leg muscles. A deep vein thrombosis (DVT) is a blood clot that forms in the veins deep in the leg, usually in the calf or thigh, although DVT can occur in other veins including the pelvis and rarely in the arms [1, 2]. DVT can partially or completely block blood flow through a vein but not everyone with DVT will experience symptoms [2].

Doctors refer to DVT as distal or proximal; distal DVT refers to DVT of the calf, proximal DVT refers to DVT above the knee and above a major vein called the popliteal vein [3]. Most DVT form in the calf area and many do not cause any symptoms. Proximal DVT is more serious than distal DVT. One in two people with untreated proximal DVT will develop symptomatic PE within 3 months [3].


Symptoms of DVT

In many cases of DVT, the clots are small and do not cause any symptoms [3]. Most patients have symptoms when there is proximal vein involvement and these symptoms can include [2]:

  • Swelling—this is usually different from the mild ankle swelling that many people get during long haul flights and the entire leg can swell
  • Pain or tenderness of the leg that is noticeable or may be worse when standing or walking
  • Discolouration of the leg, which can appear a blue or red
  • A feeling of increased warmth in the leg

Always talk to your doctor if you have any concerns about DVT or if you think you have symptoms of DVT.

Is DVT common?

Each year, about one in 1200 people in Australia and New Zealand are affected by VTE [4,7]. DVT became well known several years ago because of its association with flying for long periods (often called ‘traveller’s thrombosis’ or ‘economy class syndrome’), but the risk of getting a DVT is higher in hospitalised patients. Only about one in 6000 people who go on a long flight (more than 4 hours) will develop DVT [5], but if you are in hospital particularly for a major operation or because of a serious illness, your risk of having a blood clot in your leg or lungs is much higher than usual [1]. Hospitalised patients are over 100 times more likely to develop a DVT or PE compared with the rest of the community [6].

Complications of DVT

A DVT may not cause further problems, but complications of DVT can occur. These include:

  • Pulmonary embolism (PE)—when part of the clot breaks off and blocks blood flow to a lung [1]
  • Recurrence—despite treatment, DVT can recur [3]
  • Post-thrombotic syndrome—characterised by pooling of blood, chronic leg swelling, pain, discoloration of the skin, and leg ulcers [1, 2]; about 10% of cases with symptomatic DVT will suffer severe post-thrombotic syndrome within 5 years [3]


  1. National Health and Medical Research Council. Blood Clots: Reducing Your Risk. Melbourne; 2010. Accessed 5 November 2018
  2. Cleveland Clinic. Deep Vein Thrombosis (DVT). Accessed 5 November 2018
  3. Ho WK. Deep vein thrombosis. Australian Family Physician 2010; 39:468-74.
  4. Ho WK et al. The incidence of venous thromboembolism: a prospective, community based study in Perth, Western Australia. Med J Aust 2008; 189:144–7.
  5. World Health Organisation. 2007. Who Research Into Global Hazards of Travel (WRIGHT) Project, Final Report of Phase I. Accessed 5 November 2018
  6. Australian Commission on Safety and Quality in Health Care. Accessed 5 November 2018
  7. National Policy Framework:VTE Prevention in Adult Hospitalised Patients in NZ. Accessed 5 November 2018