Deep vein thrombosis occurs when a blood clot (also called thrombus) forms in one or more of the deep veins in your body, usually in your legs.
Blood clot formation is a normal process in the body that prevents you from bleeding too much when a blood vessel is injured. Sometimes, blood clots form within a blood vessel and may become lodged in veins deep inside the muscle – this is known as deep vein thrombosis (DVT).
The most common veins that are affected are those in the legs. The clot will either partially or completely block the flow of blood through the affected vein, causing swelling and discomfort.
DVT is a serious condition because blood clots in your veins can break loose, travel through your bloodstream and lodge in your lungs, blocking blood flow. This is called pulmonary embolism (or PE) and can be fatal.
Who is at risk of developing DVT?
Many factors can increase your risk of developing DVT. The more risk factors you have, the greater your risk.
|Risk factors for DVT
|Being inactive for long periods of time
- Bedrest for long periods of time causes reduced blood flow in your veins.
- Sitting for long periods of time such as when flying, driving or at a desk.
|Surgery and injury (trauma)
- Major surgery or operation especially of the pelvis, abdomen (tummy), hip or knee, or a bone fracture.
- Having a catheter (tube in your vein) in a big vein such as a PICC line, central venous catheter, or port.
- Read more about hospital-related DVT
|Increased hormones (oestrogen and progestin)
- Birth control pills
- Hormone replacement therapy (HRT)
- Pregnancy, including up to 6 weeks after giving birth
- Having cancer
- Heart failure
- Inflammatory disorders such as lupus, rheumatoid arthritis,
inflammatory bowel disease
- The kidney disorder called nephrotic syndrome
- Being overweight or obese – this increases pressure in the veins
- Smoking – affects blood clotting and circulation
- Age – although DVT can occur at any age, being over 60 years increases your risk
- Having varicose veins
- Genetic clotting disorder
- If you or someone in your family has had DVT or pulmonary embolism before, you're more likely to develop DVT
What are the symptoms of DVT?
A DVT can occur in any limb but tends to occur more commonly in the leg, involving the foot, ankle, calf, or whole leg.
Signs and symptoms can include:
- Swelling in the affected limb. Rarely, there may be swelling in both legs.
- Pain in your leg. The pain often starts in your calf and can feel like cramping or a soreness.
- Change of colour in the leg – bluish, purple or reddish skin colour.
- Feeling of warmth on the skin of the painful or, swollen area.
These symptoms may often be confused with a sprained ankle or other injury. DVT may sometimes occur without any noticeable symptoms. If you develop signs or symptoms of DVT, contact your doctor.
How is DVT diagnosed?
To diagnose DVT, your doctor will ask you questions about your symptoms. You'll also have a physical exam to check for any areas of swelling, tenderness or discoloration on your skin. Depending on how likely you are to have a blood clot, your doctor may suggest further testing, including:
- Ultrasound scan, which uses high-frequency sound waves to detect the presence of blood clots. This is a painless procedure.
- Blood test – almost all people who develop severe DVT have an elevated protein in their blood called D dimer.
How is DVT treated?
The main aim of DVT treatment is to prevent the clot from getting any bigger, and from breaking loose and causing a pulmonary embolism. After that, the goal becomes reducing your chances of deep vein thrombosis happening again. Treatment usually includes a combination of medication and compression.
Medications – anticoagulants (blood thinners)
Anticoagulant medications "thin" the blood, by decreasing its ability to clot. They prevent new clots from forming and existing clots from growing larger. Common examples of anticoagulant medications are:
You may require regular blood tests to check how well the anticoagulants are working and if dosage changes for warfarin are required. Anticoagulant treatment usually continued for at least 3 months to be fully effective in treating a DVT. In some cases, it may be required on a long-term basis.
These are special types of stockings that are made from special elastic to give support to the lower legs, encourage circulation and help to reduce swelling. This pressure helps reduce the chances that your blood will pool and clot. These stockings are worn on your legs from your feet to about the level of your knees.
How can DVT be prevented?
Although DVT cannot be prevented in all situations, there are a few measures you can take to lower your risk, such as:
- Avoid sitting for long periods of time. Elevate your legs if you are sitting for moderate periods of time.
- If you are travelling on a long journey or are bedridden in hospital there are special precautions you can take. See travel-related DVT and hospital-related DVT.
- If you smoke, quit smoking or reduce the amount that you smoke. The nicotine causes your blood
vessels to become smaller and the blood flow is decreased.
- If you are overweight, aim to reduce weight.
- Exercise regularly.
- Keep hydrated – drink 6 to 8 glasses of water a day.
Deep vein thrombosis Patient Info, UK
Deep vein thrombosis (DVT) Mayo Clinic, US
Deep Vein Thrombosis (Blood Clots) CDC, March 2016
Long journeys (more than 4 hours) by plane, train, bus, car, etc, are thought to cause a slightly increased risk of DVT. This is probably due to sitting without moving for long periods of time. Blood flows more slowly, and collects in the legs when they are hanging down. Blood flowing slowly is more likely to make a clot.
- The risk of DVT from travel is small. Research studies suggest that there is about 1 DVT for every 4,656 flights that last for 4 hours or more.
- The longer the flight, the more likely you are to develop a DVT.
It has to be stressed that the vast majority of travellers have no problems. Other risk factors are involved, so for most people the chance of developing a DVT just from a long journey is very small.
|If you develop a swollen, painful leg or breathing difficulties shortly after a long journey, see your doctor urgently.
Who is at risk of travel-related DVT?
Anyone may develop a DVT following a long journey but the risk is increased in the following groups:
- pregnant women
- women taking the pill
- people who have had a recent operation
- those over 40 years of age
- people with cardiovascular disease
- people with a family history of blood-clotting disorders
- those with a broken leg which is in plaster
- those who have had a recent severe illness such as pneumonia, or heart failure or a heart attack.
See your doctor before travelling to discuss your risk and what action is needed.
Tips to reduce your risk of travel-related DVT
Whilst travelling on a long journey, particularly on a long-haul plane trip, here are a few things you can do to reduce your risk of DVT:
- Exercise your calf and foot muscles regularly, bending and straightening your legs, feet and toes when you are seated. Repeat this every half hour or so.
- Press the balls of your feet down hard against the floor or foot rest every so often. This helps to increase the blood flow in your legs.
- Take a walk up and down the aisle every hour or so, when the seatbelt signs are not switched on.
- Make sure you have as much space as possible in front of you for your legs to move. So avoid having bags under the seat in front of you and recline your seat where possible.
- Take all opportunities to get up to stretch your legs, when there are stops in your journey.
- Keep hydrated – drink normal amounts of fluid to avoid a lack of fluid in the body (dehydration).
- Do not drink too much alcohol. Alcohol can cause dehydration and immobility.
- Do not take sleeping tablets, which cause you to remain in the same position for a long time.
Elastic compression stockings
Correctly fitted compression stockings can reduce the incidence of clot formation due to long-haul travel, by approximately 18 times in high risk people.¹
Check with your doctor if compression stockings are an option for you.
- Buy the stockings (or 'flight socks') from your pharmacy. Ask the pharmacist for advice about the correct sort. They need to be 'graduated compression' stockings, worn to the knee, with the correct amount of compression (class 1).
- The slight pressure from the stocking helps to prevent blood 'pooling' in the calf.
- Stockings do not replace the need for regular exercises. They are in addition to exercises.
- If you have any of the risk factors mentioned above, it would be wise to wear these stockings for your journey.
The use of medicines to prevent DVT caused by long haul travel is not necessary for people with no risk factors. Medications may be considered in people at high risk of developing clots.
- A single dose of enoxaparin (Clexane®) injection on the day of travel may be used to prevent travel-related DVT. But, this medicine is not funded for this use.¹
- There is currently no evidence to support the use of dabigatran or rivaroxaban for prevention of travel-related DVT.¹
- There is no evidence that aspirin is effective in preventing travel-related DVT and the risks of side effects (such as increased bruising and bleeding) outweigh the benefits of treatment.¹
After the journey
Have a little walk straight after the journey to 'get the circulation going'. Most travellers have no problems – many people get slight painless puffiness of feet and ankles after a long journey but this is not due to a DVT.
If you develop a swollen painful calf or breathing difficulties shortly after a long journey then see a doctor urgently.
Travel and blood clots Ministry of Health, NZ
Prevent DVT when you travel NHS Choices
- The use of antithrombotic medicines in general practice: a consensus statement BPAC October 2011
- Providing medical advice to travellers BPAC December 2011
- Philbrick JT, Shumate R, Siadaty MS, Becker DM. Air travel and venous thromboembolism: a systematic review. J Gen Intern Med. 2007 Jan;22(1):107-14.
Information for health professionals
The information on this page will be of most interest to clinicians (doctors, nurses, specialists, etc) and those interested in more detail.
Prevention of thromboembolic events from long haul travel
|There is a risk of venous thromboembolism (VTE) during travel, particularly with longer flights (> four hours).
- People at high risk of VTE include those with pro-thrombotic states (e.g. deficiencies of antithrombin III, protein C, protein S), a history of previous VTE, recent surgery or a significant medical illness.Inthesepeople consideration should be given to the use of:
- Correctly fitted compression stockings which reduce the incidence of VTE by approximately 18 times in high risk people
- Prophylactic low molecular weight heparin (one injection on the day of travel). There is evidence to support the use of enoxaparin, although this medicine is not funded for this indication.
- There is currently no evidence to support the use of dabigatran or rivaroxaban for VTE prophylaxis during travel. Aspirin is not adequate for prophylaxis and the risks of adverse effects (e.g. bleeding) outweigh the benefits of treatment. Routine use of prophylactic medicines for long haul travel is not necessary for people with no risk factors for VTE.
- The following advice should be given to all people who are travelling long distances:
- Sitting in an aisle seat provides more opportunity for movement. Also consider exercising leg muscles while seated and walking whenever possible.
- Ensure adequate hydration and avoid alcohol, particularly if combined with sedative medicines
- The use of antithrombotic medicines in general practice: a consensus statement. BPAC, 2011, October
Prevention of venous thromboembolism Best Practice Guidelines for Australia and New Zealand, 4th edition
VTE Prevention in Adult Hospitalized Patients in NZ National Policy Framework, June 2012
Venous thromboembolic diseases: diagnosis, management and thrombophilia testing NICE, June 2012
Regional HealthPathways NZ
Access to the following regional pathways is localised for each region and access is limited to health providers. If you do not know the login details, contact your DHB or PHO for more information: