Deep vein thrombosis is a blood clot that forms in a vein deep in the body. Blood clots occur when blood thickens and clumps together. These occur most often in the lower leg or thigh but they can occur in other parts of the body as well and can result from several things, including damage that occurs to a vein's inner lining from injuries caused by physical, chemical, or biological factors like, inflammation, or immune response. Clots also can form when blood flow is sluggish or slow, for example after surgery, traveling or laying in bed for a long time. Blood can be thicker and more likely to clot when you take hormone replacement or birth control pills. There is also an inherited condition that can increase blood clotting.
Though not everyone will have symptoms, when they do arise, symptoms include swelling of the leg or along a vein in the leg, pain or tenderness in the leg when standing or walking, increased warmth in the area of the leg that's swollen or in pain, and red or discolored skin on the leg.
If a blood clot in a deep vein breaks off it can travel through the bloodstream and is then called an embolus. When the clot travels to the lungs and blocks blood flow, the condition is called pulmonary embolism, a very serious condition that can damage the lungs and other organs in the body and cause death.
Blood clots in the thigh are more likely to break off and cause PE than blood clots in the lower leg or other parts of the body. Blood clots also can form in the veins closer to the skin's surface. However, these clots won't break off and cause PE.