Symptoms of deep vein thrombosis (DVT) occur when there is a blood clot in one of the deep veins (vessels that return blood to the heart after it has delivered oxygen to the tissues). Most commonly, deep vein thrombosis occurs in a vein of the leg, but it can also occur in other locations such as the pelvis. The most serious complication of deep vein thrombosis is pulmonary embolism, in which a blood clot breaks off of the DVT and travels through the bloodstream and becomes lodged in a blood vessel of the lung. Symptoms of DVT involve the overlying skin and include

redness,
warmth,
swelling, and
tenderness.

The involved vein can sometimes be felt as a rough or thick cord beneath the skin. The location of the symptoms depends on the location of the blood clot. It is possible for a DVT to occur without causing specific symptoms.

Causes of deep vein thrombosis (DVT)

There are many factors that can cause a blood clot in a deep vein. These include immobility of the leg, such as occurs with long airplane flights, hospitalization, or following surgery. Trauma to the lower leg also increases the risk, along with pregnancy and obesity. Conditions in which the blood is more likely than normal to clot (hypercoagulability) also increase the chance of deep vein thrombosis. Certain medications, smoking, and some medical conditions can increase the likelihood of the blood to clot.