Deep vein thrombosis is when a blood clot forms in a deep vein, usually in the leg, according to the National Heart, Lung and Blood Institute. The blood clot blocks or restricts blood flow to the area, resulting in tenderness and swelling. If the blood clot breaks off and travels to the lung or heart, it causes major damage to the organ and possibly death, according to WebMD.
Risk factors for developing deep vein thrombosis include smoking, being over age 60, being overweight and sitting for long lengths of time, such as on an airplane or after surgery, according to the Mayo Clinic. Pregnancy is also a risk factor, as it increases pressure in the leg veins. Aside from tenderness and swelling, other symptoms of deep vein thrombosis include a feeling of warmth or discolored skin in the affected leg, visible surface veins and leg fatigue.
Signs of a pulmonary embolism, which is when a blood clot breaks free and travels to the lungs, include a sudden coughing spell with or without blood, sharp chest pain, shortness of breath and severe lightheadedness. The signs and symptoms of deep vein thrombosis are usually not enough to make a diagnosis without special tests that include a duplex ultrasound, venography and magnetic resonance imaging, or MRI, according to WebMD.