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Blood-Clot Causes: Why They Develop
by Kevin O. Hwang, M.D.


Q. What are blood clots, and how do they develop?

A. When they refer to blood clots, people usually mean a solidified plug of blood that completely or partially obstructs the flow of blood through a vein or artery. A clot in a leg vein can break away and lodge in a lung vein. Sudden formation of a clot in an artery can cause a stroke or heart attack.

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There are three main causes of these clots:

  1. Certain health conditions (such as cancer or pregnancy) or medications (like birth control pills) that can make the blood components stickier.
  2. Damage to the inner surface of a vein or artery.
  3. Sluggish blood flow, such as from prolonged immobilization, which allows the slowly moving blood components to clot more easily.

An accumulation of blood in the muscle or fatty tissue, possibly appearing as a bruised lump, is not technically a clot and not usually dangerous.newsletter-graphic

is a board-certified internist and instructor at the University of Texas Health Science Center at Houston.

Last updated and/or approved: February 2011.
Original article appeared in a previous issue of the print magazine. Bio current as of that issue. This general health-care information is not meant as individual advice. Please see our disclaimer.
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