Deep venous thrombosis (DVT) is a blood clot in a deep vein of the legs. Pieces of the clot can break off and travel through the bloodstream to the lungs. The clots can cause serious symptoms and even death if they are not diagnosed and treated quickly. Even when patients with DVT receive treatment, they may develop sequelae related to impaired blood flow in the leg with the clot. For example, 1 out of 3 patients develop a condition called the post-thrombotic syndrome. Symptoms may include pain, swelling, cramping, numbness, tingling, and itching. Skin on the lower part of the leg may harden or darken. Doctors often recommend that patients with DVT wear special support hose (elastic compression stockings) to prevent these problems. The stockings provide a graduated pressure that is firmer at the bottom and looser at the top to help improve blood flow back to the heart. Unfortunately, few studies show whether the stockings actually prevent the post-thrombotic syndrome.