Blood clots and coagulation

Clotting factors are proteins found in blood that work together to make a blood clot. They are designated by Roman numerals I through XIII.¹

Blood vessels shrink so that less blood will leak out.¹

Tiny cells in the blood called platelets stick together around the wound to patch the leak. Blood proteins and platelets come together and form what is known as a fibrin clot. The clot acts like a mesh to stop the bleeding.¹

The clotting process¹

Injury or damage

Factors are activated

Vessel contracts

Platelet plug

Fibrin clot

Bleeding causes a biological "domino effect" in which a series of steps are set in motion. When your body detects a bleed, the clotting factors are switched on in a particular order, one after the other.¹

Each factor activates the next until they form a clot. This is known as the coagulation cascade.¹ Intrinsic and extrinsic pathways are 2 separate pathways that lead to the formation of a clot. The intrinsic pathway is activated early in the coagulation cascade, known as the initiation phase. The extrinsic pathway activates during the amplification phase of the coagulation cascade—increasing the number of platelets at the site of a bleed.²

Normal clotting¹

Factors are activated and begin the clotting process

All factors are activated and a clot is formed to stop bleeding

Clotting in hemophilia⁴

Factors are also activated, but 1 factor in the chain is weak or missing

Not all factors in the chain are activated and the clot cannot form properly

You can imagine the process like a row of dominoes. Each factor signals the next, all working together like a row of dominoes falling into each other.¹ If a single domino is missing in a row, dominoes will stop falling. In the same way, if a single factor is missing from the clotting process (like factor VIII or factor IX), the coagulation cascade gets interrupted and a proper clot will not form when you have a bleed.⁴

When certain blood-clotting factors are deficient or missing in a person with a bleeding disorder, the blood does not clot as it should, and it takes longer for a clot to form and for bleeding to stop.³