Thrombosis is the formation of a blood clot, called a thrombus, that blocks part or all of a blood vessel, such as a vein.
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Within moments after a finger is cut, platelets in the blood begin to gather at the injury. Platelets are tiny disc-shaped cells in the blood, much smaller than even a red blood cell. The platelets react with calcium and with other substances in the body's tissues to form a semisolid, stringy protein. The cut covers with a scab and eventually heals. For injuries like cuts, clots are good things. But when clots form inside blood vessels, the condition is called thrombosis, and it can be life threatening.
How Does Thrombosis Happen?
Thrombosis usually begins as an inflammation of the vein known as phlebitis * . Phlebitis develops when blood flows slowly or pools in veins. This usually occurs in the legs and causes injury to the walls of the vein. Just as platelets gather to form clots on cut fingers, they also may start to form clots along the injured walls of veins. People with phlebitis may experience pain and tenderness along the vein, skin discoloration, swelling and edema, a rapid pulse, and mild fever. If untreated, many people with phlebitis develop thrombosis in the inflamed vein.
There are many possible causes. Inactivity, such as sitting for long periods of time or resting in bed, is a major cause. Surgery, tumors * , and injuries to the leg also may cause thrombosis. Certain infections and cancers may alter the clotting substances in the blood and cause thrombosis.
Women are especially at risk, because the female hormone estrogen is linked to thrombosis. Pregnant women have very high levels of estrogen. Estrogen is also found in birth control pills and in the hormone replacement medications that some women use after menopause, although thromboses due to these medications are not very common.
What Are the Signs and Symptoms of Thrombosis?
The major symptoms of thrombosis are pain in the affected area and swelling, which can occur suddenly. If the thrombosis involves a leg vein, the leg also might appear red and feel warm to the touch. Veins close to the skin surface may look larger than normal and reddish-blue in color.
The biggest danger is when a clot forms in the large veins that are deep within the legs. If the blood clot grows, it may break off. The clot may then travel toward and then through the heart and block the pul-monary * artery, which is a major blood vessel, causing a pulmonary embolism * . This serious complication of thrombosis may cause death if not treated rapidly and effectively.
How Do Doctors Diagnose and Treat Thrombosis?
Doctors use several tests to determine if patients have thrombosis. They may inject a dye into the veins and then use an x-ray to look for clots. They may use an ultrasound machine, which uses sound waves to create an internal view of veins similar to an x-ray. Or they may test blood pressure above and below the suspected location of the clot to measure differences.
Thrombosis can be treated with medications that prevent the blood from clotting as easily. This can stop the clot from growing larger and lower the risk that the clot will break free and cause an embolism. Clot-dissolving drugs also may be injected into the vein. A procedure called balloon angioplasty widens the vein around the clot by inserting and inflating a small balloon that pushes out the narrow walls of the vein. Another surgery involves inserting a small, mesh tube within the vein to keep it open.
* phlebitis (fle-BY-tis) refers to inflammation of a vein.
* tumor refers to an abnormal growth of body tissue. Tumors may or may not be cancerous.
* pulmonary refers to the lungs.
* embolism is a blockage in a blood vessel caused by a blood clot, air bubble, fatty tissue, or other substance that traveled through the bloodstream from another part of the body.
For people at high risk for developing thrombosis, doctors sometimes recommend preventive measures such as the use of drugs that interfere with blood clotting and special compression stockings that help keep blood from pooling in the deep veins of the legs.
The Venous Educational Institute of North America posts information and
graphics about clots and surgical procedures at its website.