Deep vein thrombosis (DVT) is the term given to a blood clot forming and blocking one of the deep veins, usually in your leg, but sometimes in the pelvis. DVT does not refer to a blood clot of the veins that you can see on the skin surface (superficial thrombophlebitis) which is usually much less serious.

You may notice one or more of the following:

• Swelling of one of your legs
• Pain and tenderness of one of your legs (coming from inside, not the surface)
• The leg may seem a bit hotter than usual
• The veins on the surface of your leg may be more swollen than usual
• Your leg may be redder than usual, or a bit purple in colour
• Your temperature might be slightly higher than usual

If you think you may have a DVT you should contact your doctor as a matter of urgency to seek further advice.

Complications

Many times DVT will settle without major problems, but it can have serious complications and you should contact your doctor or the out of hours service as a matter of urgency.

The two main possible complications are:

Pulmonary embolism / pulmonary embolus

This is when part of the blood clot in the vein breaks off and moves up, through the heart, to become embedded in the blood vessels of lungs. This is a rare complication, but of those people who have a DVT affecting their thigh, up to one in ten may be affected. Pulmonary embolism is serious and can be fatal, and it is for this reason that we take DVT so seriously.

Post-thrombotic syndrome

This is a fairly common complication, and may affect between half and three quarters of people who have had a DVT. It varies in severity, and is more likely if the DVT affects the thigh. Post-thrombotic syndrome causes the veins to work less efficiently, resulting in varicose veins, aching and swelling, rashes and sometimes ulcers of the lower legs.

The veins are the slow moving blood vessels that return the blood to the heart from all parts of the body. The veins we are talking about here are the ones deep inside your legs and into the pelvis. Normally they have smooth walls and blood continues flowing through them. When you have a deep vein thrombosis a blood clot blocks off one of the deep veins in your leg.

DVT is more common if you:

• are over 40
• are obese (significantly overweight)
• have previously had a DVT or Pulmonary Embolism (PE)
• have one or more close family members who have had DVT or PE
• have cancer or are on treatment for cancer (especially hormone treatment)
• are on treatment for heart failure or similar problems
• have had a recent operation, especially on your hips, knees or legs
• have an inherited blood clotting disorder (rare)
• have had a stroke or are paralysed
• have been stuck in one position for some time on a long journey
• are pregnant or have recently had a baby
• are taking the oral contraceptive pill or hormone replacement therapy

Your doctor will examine you, looking for evidence supporting the diagnosis as listed under symptoms.

If your doctor suspects a DVT it is likely they will ask for further tests. In the UK these are usually done in the hospital and your doctor will arrange this urgently. These may include:

• a blood test (D-dimer blood assay)
• an ultrasound examination (Compression ultrasound)
• an X-ray with an injection into the vein (venography)

Treatment will usually be started in hospital, and involves drugs that slow the blood's natural process of clotting (anticoagulants).

Usually this starts with heparin treatment. This used to be unfractionated heparin (UFH), given in to a vein (by intravenous infusion), but there is now another form, low molecular weight heparin (LMWH), which is given by a simple injection under the skin (subcutaneous injection), that may be used.

It is likely you will be started on tablets which take a while to get into your system, but will take over from the heparin after a few days. (Such as warfarin, otherwise known as a rat poison!) Once blood tests confirm that the oral anticoagulant has reached a level that is having adequate effect on prolonging blood clotting (usually after 4-6 days), the heparin treatment will be stopped.

Under certain circumstances (such as pregnancy) the doctors may continue heparin therapy (usually by subcutaneous injection) rather than transferring to warfarin. In the case of pregnancy, warfarin may be started after the baby has been born.

Your warfarin dosage will need close monitoring with regular blood tests. Initially these will be every few days, but once the best dose for you is discovered and the blood test results stabilise, you will only need a test every few weeks.

Treatment is usually for a few months, but may be long-term if you have any risk factors that make it more likely that you will get a further DVT.

It may be suggested that you wear a support stocking (graduated elastic compression stocking), especially if your DVT was in your thigh. This helps to reduce the back pressure of blood on the leg veins and cuts down the risk of developing post-thrombotic syndrome.

You will be encouraged to take a regular walk and to keep your legs up when resting.

Looking at the list of causes, there are some which we cannot influence, but there some factors we can improve in order to reduce the likelihood of DVT or a recurrent DVT:

• Try to keep your weight in the recommended range.
• Where possible, avoid long periods of immobility.
• Stay active, take regular walks.
• If you have had a DVT while on the oral contraceptive pill or HRT, it is likely that you will be advised to avoid this in future.
• If your DVT has come on during pregnancy or in the post-natal period this does not mean that you cannot have any more babies, but you should discuss the issues around this with your doctor. This may also suggests that you may be more at risk from the oral contraceptive pill or HRT.
• If an underlying blood clotting problem (such as thrombophilia) is to blame, or there other factors that are likely to lead to an increased ongoing risk of DVT, you are likely to be kept on long-term anticoagulants.
• If you are due to have a major operation, especially on your hip or knee, the surgeon will ensure that appropriate precautions are taken, and may recommend aspirin or heparin. You may be provided with support stockings and sometimes a special inflatable sleeve attached to a pump is put round your leg during the procedure.

Precautions when travelling

If travelling a long way in a confined space, as in a plane or car:

• Get up and have a walk every now and again.
• Keep drinking plenty of fluid (not alcohol, or drinks containing caffeine, as these end up dehydrating you, which makes the blood thicker and stickier).
• Exercise your calf muscles every now and again, even when you are not getting up.
• Below knee (Class 2) support stockings may help to prevent travel-related DVT.
• There is no evidence that aspirin is effective in preventing travel-related DVT.
• If you are more at risk of developing DVT and have to take a long flight, discuss it with your family doctor.