​Deep vein thrombosis (DVT) is a blood clot (also called a thrombus) that forms in a vein deep in the body. Most deep vein clots occur in the lower leg or thigh but can also occur in other parts of the body. This clot may interfere with circulation and it may break off and travel through the blood stream and lodge in the lungs, causing severe damage to that organ. If the clot lodges in the lung, it is called pulmonary embolism. This is a very serious condition that can cause death. Symptoms of pulmonary embolism include chest pain when taking a deep breath, rapid pulse, fainting, shortness of breath and coughing up of blood. Blood clots that remain lodged in the leg can result in pain and swelling.

Only about half of the people with deep vein thrombosis have symptoms. The symptoms may include:

​The risks of developing DVT include prolonged sitting, bed rest, or immobilisation (such as on long plane or car trips), recent surgery or trauma (especially hip, knee or gynaecological surgery), fractures, childbirth within the last 6 months and the use of medications such as oestrogen and birth control pills.

​When someone goes to the A&E (the accident and emergency department of hospitals) or his general practitioner with deep vein thrombosis (DVT) symptoms, he will be put through tests such as validated scoring algorithms and the D-dimer, or CT and MRI scans.

If the condition is confirmed, the first thing to do is prevent more clots from forming, while giving the body a chance to melt the initial clot. 

If there is a large limb or life-threatening clot, a strong dose of a thrombolytic drug might have to be given to try and dissolve it, but that would put the patient at risk of bleeding. A thrombolytic drug is used to dissolve blood clots in stroke or heart attack situations. In such instances, the blood clots are very small but situated in strategic positions where they can cause massive damage. Administering thrombolytic drugs, a procedure performed by an interventional radiologist or surgeon, is not commonly done.

Hence, the usefulness of using drugs to dissolve a large blood clot has to be weighed against the risks, especially in situations where the clot has to be dissolved quickly.

If a patient diagnosed with DVT is also at high risk of developing a pulmonary embolism, but cannot use anticoagulant drugs because he is at risk of bleeding, an inferior vena cava filter may be used to prevent the blood clot from travelling towards the lungs. The filters can be removed later and anticoagulant drugs should be started as soon as the risk of bleeding subsides.

In extreme cases, surgery can be performed to remove clots, in particular life-threatening clots in the lungs.