What is deep vein thrombosis?

Deep vein thrombosis is a blood clot that develops in a large vein, usually occurring in the pelvis or the leg, but can also occur in the arm. A blood clot may occur when the cells in the blood clump together while moving through a vein. Blood thinners (anticoagulants) are used to prevent blood clots from continuing to grow and from breaking free to travel from the legs or arms to the lung.