A blood clot is the product of blood coagulation which is a mechanism whereby in case of an injury to a blood vessel, greater blood loss can be prevented. A network of fibrin, platelets and red blood cells fill the opening in the damaged vessel. Disorders of the blood clotting system can lead to an increased risk of bleeding on the one hand (reduced activity) or to the risk of a 'spontaneous' clot (thrombus) forming within an undamaged vessel (obstructive clotting or thrombosis).