In deep vein thrombosis (DVT), a blood clot (thrombus) forms in a deep-lying vein, usually in the leg. Although not dangerous in itself, part of the clot may break off and lodge in a blood vessel supplying the lungs, causing a potentially life-threatening blockage called a pulmonary embolism.
DVT is caused by a combination of slow blood flow, blood vessel damage, and an increased tendency of the blood to clot.
Risk factors include prolonged immobility, injuries such as bone fractures, surgery, dehydration, pregnancy, certain blood disorders, hormone replacement therapy or taking the combined contraceptive pill, smoking, and being overweight.
Treatment includes medication to prevent further clotting and to stop an embolism , and sometimes surgery.