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 haemostasis. During haemostasis, 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.
Once the coagulation cascade has been initiated, coagulation factors are activated one after the other in a sequential process. As the cascade nears completion, soluble fibrinogen (fibrinogen dissolved in fluid) is changed into insoluble fibrin threads. These threads crosslink together to form a fibrin net that then stabilises at the injury site. The fibrin net adheres to the site of injury along with aggregated cell fragments called platelets to form a stable blood clot. This barrier prevents additional blood loss and remains in place until the injured area has healed. Haemostasis is a dynamic process, though, so once a clot is formed, other factors are activated to slow the clotting process. They eventually begin to dissolve the clot in a process called fibrinolysis so that the clot is removed when the injury site is healed. In normal, healthy individuals, this balance between clot formation and dissolution ensures that bleeding does not become excessive and that clots are removed once they are no longer needed.
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 surgery, dental procedures, or trauma. Bleeding disorders can be congenital (present from birth) or acquired (occurring in later life due to a trigger such as infection). Bleeding disorders may cause symptoms that range from nosebleeds, bleeding gums, bruising, heavy menstrual periods, blood in the stool and/or urine to arthritic-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 of 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).