When a blood vessel or tissue is injured and starts to bleed, a process called haemostasis is started by the body to create a blood clot to restrict and eventually stop the bleeding. This process produces fibrin threads which is a protein which links with the haemostasis to form a fibrin net. That net along with the platelets, helps hold the creation blood clot in place at the injury until the wound is healed. Once the injury is healed and a clot is no longer needed, the body uses plasmin, an enzyme to break the thrombus (clot) into small pieces so that it can be removed. The pieces of the disintegrating fibrin in the clot are called fibrin degradation products (FDP), which consist of variously sized pieces of crosslinked fibrin. One of the final fibrin degradation products produced is D-dimer. The level of D-dimer in the blood can significantly rise when there is a critical formation and breakdown of fibrin clots in the body.For a person who is at low or intermediate risk for blood clotting and/or thrombotic embolism, the strength of the D-dimer can help determine the strength of the fibrin and if needed, the person can be hospitalised.