Deep-vein thrombosis is the condition is which blood clots form in veins, usually in the legs. Risk factors include:

In the case of a thrombus in the leg, symptoms and risks vary, depending on where the clot is. Clots in other areas are rare, and may cause no obvious symptoms.

In the case of a clot in the popliteal or tibial veins, there is usually some calf pain, although there will not be much swelling.

If the blockage occurs in the femoral vein, the condition is more serious, and there will be significant calf and thigh pain, accompanied with swelling below the knee.

A clot in the Iliac vein is most serious of all, as this will restrict blood flow from the whole leg, and there will be swelling and pain over the entire limb.

While there are risks from these problems, it is not these that lead to DVT being a condition about people worry. If the clot breaks free, and ends up in the heart, lungs or brain there may be very serious consequences, possibly including death.

When DVT is suspected is can be diagnosed with an ultrasound scan. In minor cases anticoagulant drugs are given, and the clot will be broken down by the body. In more serious cases, where there is risk of the clot breaking off an operation known as a thrombectomy will be necessary.