SummaryRead the full fact sheet
- Deep vein thrombosis is where a blood clot forms in the deep veins of the leg.
- Complications can include a blood clot in the lungs (pulmonary embolus), inflammation of the vein (phlebitis) and leg ulcers.
- Medicines are usually needed to treat deep vein thrombosis and to prevent further blood clots.
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About deep vein thrombosis
Deep vein thrombosis (DVT) is where a blood clot forms in the deep veins of the leg (veins below the skin’s surface that are not visible through the skin).
The term ‘thrombosis’ refers to the formation of a blood clot in a blood vessel. When this happens, the clot can block the flow of blood and oxygen to parts of the body, which can cause potentially serious health effects.
Blood flow through the leg veins generally requires help from calf muscles. When the calf muscles contract, they compress the veins and force the blood upwards to the heart (against gravity). Valves in the veins also help this process, ensuring the blood flows in one direction.
Anything that slows the flow of blood through the deep veins in the legs can cause DVT. This includes an injury, surgery or long periods of sitting or lying.
Sometimes a blood clot can travel from the leg and lodge in a blood vessel in the lungs. When this happens, it is called a pulmonary embolus. If the clot is large enough, it can completely block the blood vessel and in some cases can cause death.
Blood clotting and DVT
Blood contains platelets and compounds called clotting factors. Platelets are sticky and help the blood to thicken (coagulate), which is a normal part of wound healing.
When you get a cut or scratch, platelets collect at the site of the injury. Together with clotting factors, the platelets produce a web or mesh, which traps more platelets and creates a plug to seal off the wound.
The ability of the blood to clot is essential for survival, but when it stops blood from flowing properly, it can cause problems.
Risk factors for DVT
DVT is more likely to happen if you:
- have coronary heart disease
- are over 40
- have obesity
- smoke tobacco
- have had DVT before or have a family history of blood clots or stroke at a young age
- take the contraceptive pill or hormone replacement therapy
- have cancer or heart failure
- have varicose veins
- have a blood clotting disorder.
There are also some temporary situations that can increase the risk of DVT. These include if you:
- have had major surgery
- have had an injury (fractures, spinal cord injuries, muscle injuries)
- are confined to bed or have limited movement
- go on a long journey (more than four hours) by plane, car or train
- are pregnant or if you've had a baby in the previous six weeks
- are dehydrated
- have an infection.
Sometimes DVT can happen for no obvious reason.
Long distance travel and DVT
Long distance travel by air, road or rail for longer than four hours is associated with an increased risk of DVT in susceptible people. To help reduce the risk of DVT while travelling long distances:
- wear loose clothes
- drink plenty of water
- sit with your legs uncrossed
- move about whenever possible before, during, and after travelling
- do some simple leg and foot stretches every couple of hours to keep your calf muscles active when you’re sitting
- avoid tobacco smoking and alcohol.
If you have any risk factors for DVT, speak with your doctor before travelling. Some people may benefit from wearing compression stockings, so speak to your doctor to understand if this is suitable for you.
If you are on medicines to prevent blood clots, such as anticoagulants, be sure to follow your doctor’s recommendations when traveling.
Symptoms of DVT
The symptoms of DVT usually affect one leg (rarely both) and can include:
- throbbing, pain, cramping and tenderness (usually in the calf or thigh)
- pain on extending the foot
- swelling of the lower leg, ankle and foot
- skin that is warm to touch
- changes in skin colour of the leg (red, pale or blue).
These symptoms can also happen in your arm or tummy if that's where the blood clot is.
Diagnosis of DVT
It’s important to get medical help as soon as possible if you think you have DVT.
If a doctor thinks you have DVT, you will be referred for an ultrasound as soon as possible (usually within 24 hours). An ultrasound shows if blood is flowing normally through the veins, or if there is a blockage.
You may also have an X-ray of the vein (venogram). Dye is injected into the foot and X-rays of the leg veins are taken to see if there is a blockage.
Your doctor may also arrange blood tests, like a D-dimer blood test. Blood clots produce a protein called D-dimer. If the D-dimer test is negative, this can help rule out DVT.
Treatment for DVT
You may have an injection of an anticoagulant medicine while you're waiting for an ultrasound scan to tell if you have DVT.
After DVT is diagnosed, the main treatment is an anticoagulant medicine (in tablet form), which you will probably need to take for at least six weeks.
Other treatments involve breaking up and sucking out the clot through a small tube in the vein, but this is not suitable for everyone.
It is important to manage risk factors to prevent further blood clots after DVT. Talk to your doctor about your reducing your risk. Stopping smoking and maintaining a healthy weight can help prevent DVT.
For some people, your doctor may talk to you about a test for antiphospholipid syndrome, a blood disorder that puts a person at greater risk of developing blood clots.
Complications of DVT
If DVT isn’t treated, it can cause complications, including inflammation of the vein (phlebitis), leg ulcers and pulmonary embolism.
Pulmonary embolism is the most serious complication of DVT. It happens when the clot leaves the leg vein and travels through the blood vessel system to the lungs. When the clot lodges in the lungs, it can block the main artery to the lungs or one of its major branches. When this happens, the lung tissue is starved of blood and oxygen.
It’s estimated that around one third of people who experience a major pulmonary embolism will die. Life-saving treatment for pulmonary embolism includes medicines to dissolve the clot and restore blood flow.
Prevention of DVT
In hospital, compression stockings can decrease the risk of DVT.
The use of anticoagulant medicines to prevent clots forming in the first place are recommended in people considered to be at moderate to high risk of DVT.
If taking anticoagulant medicines, check with your doctor or pharmacist before you take any other medicine (including over-the-counter medicines). Other medicines can interact with anticoagulant medicines.
Other ways to reduce the risk of DVT include stopping smoking, being physically active, following a heart-healthy eating pattern and maintaining a healthy weight.
Where to get help
- In an emergency, always call Triple Zero (000)
- Emergency department of your nearest hospital
- Your GP (doctor)
- NURSE-ON-CALL Tel. 1300 60 60 24 – for expert health information and advice 24 hours a day, 7 days a week
- Thrombosis Australia (TA) is an initiative of the Perth Blood Institute (PBI), a not-for-profit organisation dedicated to improving the quality of life for people with blood disorders.
- Centers for Disease Control and Prevention. Blood clots and travel: what you need to know. 2022.
- Clarke MJ, Broderick C, Hopewell S, Juszczak E, Eisinga A. Compression stockings for preventing deep vein thrombosis in airline passengers. Cochrane Database Syst Rev. 2021;(4):CD004002. doi: 10.1002/14651858.CD004002.pub4.
- Johnson IM, Shatzel J, Olson S, Kohl T, Hamilton A, DeLoughery TG. Travel-associated venous thromboembolism. Wilderness Environ Med. 2022;33(2):169-178. doi: 10.1016/j.wem.2022.02.004
- Tran HA, Gibss H, Merriman E, Curnow JL, Young L, Bennett A et al. New guidelines from the Thrombosis and Haemostasis Society of Australia and New Zealand for the diagnosis and management of venous thromboembolism. Med J Aust. 2019;210(5):227-235. doi: 10.5694/mja2.50004