Deep vein thrombosis (DVT) - A blood clot that forms in a vein deep in the body.
Blood clots occur when blood thickens and clumps together.
Most deep vein blood clots occur in the lower leg or thigh, but also can occur in other parts of the body.
A pulmonary embolism (PE) is a blood clot in a deep vein that breaks off, travels through the bloodstream to the lungs, and blocks blood flow. PE is a very serious condition that can cause death. Blood clots in the thigh are more likely to break off and cause pulmonary embolism (PE) than blood clots in the lower leg or other parts of the body.

Blood clots can form in deep veins when:

• Damage occurs to a vein's inner lining from injuries caused by physical, chemical, or biological factors such as surgery, serious injury, inflammation, and an immune response.
• Blood flow is sluggish or slow from lack of motion occurring after surgery, if you're ill and in bed for a long time, or if you're traveling for a long time.
• Your blood is thicker or more likely to clot than normal.

Risk Factors
Risk factors increases if you have more than one risk factor:

• A history of deep vein thrombosis (DVT).
• Certain inherited conditions (such as factor V Leiden) increase blood's tendency to clot. This also is true of treatment with hormone replacement therapy or birth control pills.
• Injury to a deep vein from surgery, a broken bone, or other trauma.
• Slow blood flow in a deep vein from lack of movement.
• Pregnancy and the first 6 weeks after giving birth.
• Recent or ongoing treatment for cancer.
• A central venous catheter. This is a tube placed in a vein to allow easy access to the bloodstream for medical treatment.
• Being older than 60 (although DVT can occur at any age).
• Being overweight or obese.

Only about half of the people who have DVT have signs or symptoms:

• Swelling of the leg or along a vein in the leg.
• Pain or tenderness in the leg, which you may feel only when standing or walking.
• Increased warmth in the area of the leg that's swollen or in pain.
• Red or discolored skin on the leg.

Other symptoms may relate to pulmonary embolism (PE):

• Unexplained shortness of breath.
• Pain with deep breathing.
• Coughing up blood.
• Rapid breathing and a fast heart rate.

DVT is treated with medicines that thin the blood, interfere with the blood clotting process, and dissolve blood clots.
Other treatments include filters to catch blood clots and compression stockings that prevent blood from pooling and clotting.
Prevention of Deep Vein Thrombosis

• See your doctor regularly.
• Follow treatment plan your doctor prescribes.
• Stay active if possible.
• Exercise your lower leg muscles during long trips.
  I heard Dr. Oz say on one of his TV shows that if you sit for more than a couple hours at any location, it is a risk for deep vein thrombosis. He says he takes an aspirin right before he flies on an airplane.