What is it?
A bleeding disorder is an acquired or inherited tendency to bleed excessively. Normally, blood remains in the circulatory system inside the blood vessels. However, if veins or arteries are injured, they will begin to leak blood, either externally or into body tissues. The body stops the blood loss through a complex clotting process called hemostasis. During hemostasis, the injured blood vessel constricts to reduce blood flow, platelets adhere to the injury site and clump together to form a loose platelet plug, and a process of clot formation called the coagulation cascade is initiated.
The coagulation cascade has two branches: if the damage is to tissue, the body responds by activating the extrinsic pathway. If the injury is to a blood vessel wall, the intrinsic pathway is activated. Each of these pathways utilises different coagulation factors, proteins that are carried in an inactive form in the blood. These factors are sequentially activated down one pathway or the other and come together to complete the clotting process in the common pathway. By the end of the cascade, insoluble fibrin threads have been formed, woven through the platelet plug, crosslinked to make a fibrin net, and stabilised at the injury site. The resulting stable blood clot creates a barrier that prevents additional blood loss and remains in place until the area has healed. When the clot is no longer needed, other factors are activated to dissolve and remove it.
Bleeding disorders occur when something goes wrong with the clotting process. If a component is missing, deficient, or dysfunctional, excessive bleeding may occur. Such bleeding may be severe, with bleeding episodes beginning in early childhood, or mild – involving bleeding for an extended period of time following a surgery, dental procedure, or trauma. Bleeding disorders may cause symptoms that range from nosebleeds, bleeding gums, bruising, heavy menstrual periods, and blood in the stool and urine to arthritis type symptoms (damage from bleeding into joints), loss of vision, and chronic anaemia.
Abnormalities may involve: the structure of the blood vessels, the production or function of one or more of the coagulation factors, the development of antibodies against one or more of the factors, the production or function of the platelets, and/or the integrity and stability of the blood clot. Inherited bleeding disorders are rare and tend to be caused by a deficiency or dysfunction in a single coagulation factor or clotting component.
The most common are Haemophilia A (factor VIII deficiency) and von Willebrand’s disease (von Willebrand factor is a protein that helps platelets adhere to the injury site). Acquired bleeding disorders are varied and occur more frequently than inherited disorders. Common ones include multiple factor deficiencies caused by liver disease or vitamin K deficiency (since many coagulation factors are produced in the liver and several are vitamin K dependent) and factor inhibitors (especially factor VIII inhibitor – an antibody against factor VIII).
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