Factor V (pronounced factor five) is a protein of the coagulation system, rarely referred to as proaccelerin or labile factor. In contrast to most other coagulation factors, it is not enzymatically active but functions as a cofactor.

Its a protein made in your liver that helps convert prothrombin into thrombin. This is an important step in the blood clotting process. If you don’t have enough factor V or if it doesn’t work properly, your blood may not clot effectively enough to stop you from bleeding. There are different levels of severity of factor V deficiency based on how little or how much factor V is available to the body.

see Factor V deficiency.