Deep Vein Thrombosis (DVT) is a blood clot (thrombus) in a deep vein, usually in a leg vein, but it can occur elsewhere. Veins are blood vessels, which take blood towards the heart. Deep veins pass through the centre of the leg and are surrounded by the muscles.
When you have a DVT the blood flow in the vein can be partially or completely blocked, depending on whether the blood clot partially or completely fills the width of the vein.
A DVT is different to blood clots that form in a separate set of veins (called superficial veins) that lie under the skin. These clots are called superficial thrombophlebitis and are much less serious.
It is estimated that about 1 in 2000 people have a DVT each year in the UK. This ranges from less than 1 in 3000 in people under the age of 40 years to up to 1 in 500 in those over 80 years.
DVT can be very serious. When a blood clot forms in a leg vein it usually remains stuck to the vein wall. The symptoms tend to settle gradually. Complication can occur but are usually prevented if you are given anticoagulation treatment. Complication are:-
Pulmonary embolus:- In a relatively small number of people who have a DVT, part of the blood clot breaks off; this becomes an embolus (any object causing an obstruction in the vein). This travels through the bloodstream. An embolus will travel in the bloodstream until it becomes stuck. An embolus that comes from a clot in a leg vein will travel up the larger leg and body veins to the heart, through the heart chambers, but will get stuck in a blood vessel going to a lung. This then becomes a pulmonary embolus.
Some pulmonary embolus may not cause any symptoms or they can cause breathing problems and chest pain. In some cases a pulmonary embolus can cause collapse and sudden death. It is estimated that about 1 in 10 people with an untreated DVT develop a pulmonary embolus large enough to cause symptoms or death.
Post-thrombotic syndrome: - Without any treatment, up to 6 in 10 people who have a DVT develop long-term symptoms. This is known as 'post-thrombotic syndrome'. Symptoms occur because the increased flow and pressure of the diverted blood in other veins can affect the tissues of the calf. Symptoms can range from mild to severe and include: calf pain, discomfort, swelling, and rashes. An ulcer on the skin of the calf may develop in severe cases.
Post-thrombotic syndrome is more likely to occur if the DVT occurs in a thigh vein, or extends up into a thigh vein from a calf vein. It is also more common in people who are overweight, and in those who have had more than one DVT in the same leg.