A blood clot that forms in the veins (a venous blood clot) is considered a peripheral venous disorder. These may not be life-threatening, but can result in pain and discomfort or, in some cases, serious medical conditions. Peripheral venous disorders include:

• Thrombophlebitis. An obstructing blood clot has formed, causing the surrounding vein to become inflamed (phlebitis). If the blood clot formed in a superficial vein near the surface of the skin, it is called superficial vein thrombosis. If the blood clot formed in a deeper vein, it is called deep vein thrombosis (DVT). Deep vein thrombosis is a major risk factor for pulmonary embolism. This is because the clot may break off (embolize), travel through the return circulation, pass through the right side of the heart and into the lungs, where it may cause an obstruction.
  
  
• Varicose veins. A blood clot can damage the valves within a vein. The valves are responsible for keeping blood flowing smoothly in the right direction, which is particularly important when the veins are counteracting the effects of gravity to bring oxygen–poor blood from the legs to the heart. The valves close between heartbeats to keep blood from flowing backward in the wrong direction (regurgitation). Leaky or damaged valves can cause blood to pool in the legs, resulting in swollen, varicose veins.



• Thrombotic thrombocytopenic purpura (TTP). A condition in which a lack of platelets can lead to the formation of small blood clots throughout the body. It can cause widespread damage to many organs.

There are many other conditions related to blood clots, and their names usually refer to the area of the body where the clot occurs. Coronary thrombosis, for example, is a blood clot in one of the coronary arteries. Mesenteric venous thrombosis is a blood clot in the mesenteric vein (either of two veins draining the intestine), and retinal vein occlusion refers to a blood clot in a vein of the eye.