What is a thrombus?

• A. Clot of platelets, fibrin and blood cells on a vessel wall
• B. A traveling clot released into the bloodstream
• C. An infection within a blood vessel
• D. A rupture of a vessel wall

Answer: (A)

A thrombus is a clot that forms in place on a vessel wall as part of the body's coagulation process. It’s made up of platelets, fibrin, and trapped blood cells, and it stays attached to the vessel where it formed. This distinguishes it from an embolus, which is a thrombus that has broken free and traveled through the bloodstream to lodge elsewhere. A thrombus is not an infection within a blood vessel, nor is it a rupture of a vessel wall that causes bleeding. Recognizing that a thrombus is an in-situ clot adherent to the vessel wall helps explain why it can impede blood flow at its site and why embolization can lead to downstream obstruction.