A thrombosis is the formation of a blood clot in a blood vessel. DVT often begins in the calf or thigh because blood moves relatively slowly in these areas, particularly if exercise is limited. As the blood begins to pool in an area, a clot develops and can attach itself to the wall of a vessel or in more severe cases become wedged within a vessel, blocking blood flow.
Blood clots are common.
And while a blood clot itself is not life threatening it can cause serious complications. Professor Reginald Lord, head of the vascular group of St. Vincent's hospital in Sydney, says only one percent of venous thromboses cause complications. As a clot develops in size, it can shed pieces of the clot. These are referred to as emboli. The emboli float through the blood system and can travel through the heart to major arteries in the lung causing serious and sometimes fatal complications.