DVT occurs because of blood clotting in deep veins of the body, most frequently in the large veins of the calves.

Sometimes these clots break free and travel up the veins through the heart to lodge in the arteries of the lungs. This related condition is known as pulmonary embolism (PE), and it may cause sharp chest pain or breathlessness. PE may be life-threatening if the embolus (circulating clot) is large.

Causes of DVT

DVT may occur when the blood pools in the deep veins in your legs, when there is some factor that makes your blood more likely to clot or when there is damage to the vein wall. The blood will pool if the flow is interrupted. This may happen because there is compression of the vessel so the vein is narrower, or if the normal ‘muscle pump’ of the leg is not pumping blood back to the heart.

For example, when you are bedridden (after surgery) or when you sit still for prolonged periods (such as during a long aeroplane flight) your blood tends to pool. Blood pools in the larger veins of your legs and clots may form. Injury, certain kinds of major illness and some medications also increase the tendency for blood to clot. (See risk factors below)


About half of people with deep-vein thrombosis have no symptoms. These are so-called “silent” DVT’s and may resolve on their own or progress to pulmonary embolism. If symptoms do occur, they typically occur in one leg only and include:

    • Swelling in the calf, ankle, foot or (rarely) the thigh

    • Increased warmth of the calf or other affected area

    • Tenderness to touch

    • Pain in the calf or behind the knee

    • Leg cramps at night

    • The affected skin is slightly redder than normal. A bluish tinge means major blockage.

    • Pain when bearing weight on the leg

    • A sharp pain in your calf when your foot is flexed upward

    • Slightly elevated temperature (37,5 degrees C)

Who’s at risk?

Deep-vein thrombosis occurs in approximately two out of 1 000 people and is most commonly seen in adults over age 60. Conditions and circumstances that increase your risk of developing DVT include:

    • Obesity

    • Smoking

    • Pregnancy

    • The use of oral contraceptives or hormone replacement therapy

    • Post-surgery, especially orthopaedic (lower limbs), gynaecological or heart surgery

    • Cancer

    • Lower limb injury or surgery

    • Family history of DVT

    • Previous thrombosis or embolism

    • Recent surgery or trauma

    • Fractures of the hip, femur (thigh bone) or lower leg

    • Being bedridden or in a wheelchair

    • Stroke

    • Heart attack


Your doctor will take your medical history and perform a physical examination. However, further tests are needed to confirm the diagnosis of deep-vein thrombosis because the symptoms are often similar to those of other conditions. Common tests include:

    • Duplex Doppler is a combination of ultrasound (which uses high-frequency sound waves to create an image of the leg veins) and a flow ‘probe’ which shows the direction of the flow of the blood in the veins. This combination will show any blockage in the veins.

    • Contrast venography involves injecting a substance into the veins that shows up on X-ray.

Blood clots are sometimes discovered on performing a CT (computerised tomography) scan of the pelvis. A sample of your blood may also be sent to the laboratory to test for conditions that cause increased blood clotting tendency.


Treatment usually requires hospitalisation and bed rest, at least initially. However, prolonged sitting in one position is to be avoided. A combination of anticoagulant medications, which 'thin' the blood in order to prevent further clots, is used at first. Regular blood tests tell your doctor when these drugs are working correctly.

Your doctor will prescribe and monitor suitable medication.

Leg compression devices are often used to prevent DVT while you are in hospital. The leg may be elevated to reduce swelling. Warm, moist heat can be applied to the affected area to relieve pain.

In rare cases, the clot may need to be surgically removed.


General health measures (taking regular exercise, giving up smoking and controlling your weight) can help lower your overall risk for deep-vein thrombosis. For people who have had DVT or are at risk of developing of DVT, the following prevention measures are recommended:

    • Avoid prolonged bed rest or immobility of the legs. Leg exercises help to prevent pooling of blood in the legs. Walking as soon as possible after surgery will help lower your risk of DVT. If you are unable to exercise, your caregiver should massage your legs and perform passive exercises on them within their range of motion.

    • Ask your doctor or pharmacist about special supportive elastic stockings. Ensure the stockings fit smoothly and firmly but are not too tight in any one area as this can block blood flow. Remove them once a day to wash them and to check the skin for discoloration or irritation.

    • Keep your legs elevated when you are lying or sitting down to promote the return of blood through the leg veins.

For air travelers:

    • Drink plenty of (non-alcoholic) fluids during flights

    • Regularly mobilise the ankles and massage the calves while you are sitting

    • Wear loose, non-restrictive clothing

    • Avoid taking sleeping tablets as these will make cause you to move less while you sleep during flight

    • Be vigilant for the symptoms of DVT, in particular pain in the calves, during and for up to a month after long flights.

Image via Thinkstock