A DVT is the formation of a blood clot in a deep vein, usually in the lower leg. In some cases, a DVT can form in the arm, or deep veins of the pelvis. One of the main predisposing factors for DVT is immobility (hence the association with long-haul flights), but trauma to the leg veins following a fracture or surgery and clotting abnormalities of the blood can also lead to the development of clots (thrombi).

There are many risk factors for deep vein thrombosis and these can be divided into strong, moderate and weak.

Strong risk factors:

• Fracture of hip or leg
• Hip or knee replacement
• Major general surgery
• Major trauma
• Spinal cord injury

Moderate risk factors:

• Previous DVT
• Clotting disorders of the blood
• Malignancy
• Pregnancy
• Oral contraceptives and hormone replacement therapy
• Heart or respiratory failure
• Intravenous drug abuse

Weak risk factors:

• Increasing age
• Staying in bed for longer than three days
• Obesity
• Prolonged car or plane travel
• Varicose veins
• Laparoscopic surgery

In some cases of DVT, there may be very few, if any, symptoms. However, when symptoms do show they can include:

• Pain and swelling in the leg, often in the calf
• The skin feeling warmer where the clot has formed
• The skin becoming red below the back of the knee
• Aching in the area affected

If you are suspected of suffering from DVT it is common for your GP to recommend a specialised blood test called a D-dimer test. This test identifies pieces of blood clots that are loose in your bloodstream after breaking down.

If you have a large number of pieces of blood clot in your bloodstream, this is a sign that a blood clot is present in the vein. However, the reliability of this test has been called into question because there is always the possibility of blood clot fragments increasing in number either following an injury, after an operation or during pregnancy. Often an ultrasound scan or similar tests will be required to confirm DVT.

Serious complications can arise if DVT is misdiagnosed or doesn’t receive the recommended medical treatment. These include:

• Pulmonary embolism
• Post thrombotic syndrome
• Chronic venous insufficiency
• Amputation
• Death

Pulmonary embolism is a very serious condition that can develop if DVT is not treated correctly. If you suffer from a pulmonary embolism you may experience breathlessness, pain in the chest while breathing and it may even cause you to collapse suddenly.

If you or someone you know shows signs of pulmonary embolism you should seek medical attention immediately.