How Blood Clots: Coagulation
The Way Blood Clots:
Blood clotting, or coagulation, is the process that controls bleeding when a blood vessel is injured. This process involves proteins or blood clotting factors. Normally, a complex process occurs using these clotting factors that trigger the formation of a fibrin clot that stops bleeding.1,2
Normal clotting sequence.
Interrupted clotting sequence.
When a person whose blood factor levels are normal experiences bleeding (i.e. due to a blood vessel wall injury), the following series of events are set in motion:1
Blood vessels shrink so that less blood will leak out.1,3
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.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.3,4
In a person with von Willebrand disease (vWD), they either don’t have enough of the clotting protein, von Willebrand factor (VWF), or the VWF they do have doesn’t work properly. The role of VWF is to make platelets stick to the wall of an injured blood vessel and to each other. However, if a person doesn’t have enough VWF or it doesn’t work properly, a platelet plug can’t form.5
VWF is also considered a carrier protein, meaning that it carries clotting factor VIII with it. When there isn’t enough—or any—VWF, factor VIII gets broken down in the bloodstream and there may not be enough of it to stop a bleed.5
When someone has hemophilia, they either have low levels of clotting factors or none at all.6 Hemophilia A is characterized by a lack or decreased amount of clotting factor VIII, while hemophilia B is caused by a lack or decreased amount of clotting factor IX.6
Treatment is available for both hemophilia and vWD, which may involve infusing the missing factors into the patient to help their blood clot.5,6
- The clotting process. World Federation of Hemophilia website. http://www.wfh.org/en/page.aspx?pid=635. Updated January 2014. Accessed May 10, 2018.
- What are rare clotting factor deficiencies? World Federation of Hemophilia website. https://www.wfh.org/en/page.aspx?pid=662. Updated May 2014. Accessed May 10, 2018.
- What happens when a person bleeds. Steps for Living website. https://stepsforliving.hemophilia.org/basics-of-bleeding-disorders/what-happens-when-a-person-bleeds. Accessed May 10, 2018.
- What are rare clotting factor deficiencies? World Federation of Hemophilia. http://www1.wfh.org/publication/files/pdf-1337.pdf. Accessed May 10, 2018.
- The basics of bleeding disorders: von Willebrand disease. Steps for Living website. https://stepsforliving.hemophilia.org/basics-of-bleeding-disorders/types-of-bleeding-disorders/von-willebrand-disease. Accessed May 10, 2018.
- The Basics of Bleeding Disorders: Hemophilia. Steps for Living website. https://stepsforliving.hemophilia.org/basics-of-bleeding-disorders/types-of-bleeding-disorders/hemophilia. Accessed May 10, 2018.