Definition of "prothrombin" [prothrombin]

• A plasma protein that is converted into thrombin during blood clotting. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Vitamin K – It is essential for the production of prothrombin, which is responsible for the clotting of blood."
• "A test called prothrombin time PT may be used to determine whether or not your liver is producing these blood-clotting factors adequately."
• "Clotting studies, such as prothrombin time (PT) and partial thromboplastin time (PTT): These tests measure the time it takes for blood to clot."