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Blood clot in a vein

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Blood clot in a vein

Blood clot forming.

A blood clot can form when the valves in the veins do not work properly. If the valves do not open normally, blood cells can collect behind the valve and begin to stick together to form a clot. A collection of clotted blood cells is called a thrombus.

The clot, or a piece of it, can break off and travel through the blood vessels. A blood clot can cause serious problems if it gets stuck in a vein and blocks blood flow (thromboembolus).

Current as of: May 1, 2026

Author: WebMD Ignite Staff
Clinical Review Board
All WebMD Ignite education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

Current as of: May 1, 2026

Author: WebMD Ignite Staff

Clinical Review Board
All WebMD Ignite education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

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This information does not replace the advice of a doctor. WebMD Ignite, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Learn how we develop our content.

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