A blood clot is a mass of blood that forms when blood cells and other substances in the blood clump together. Clotting is a normal process that helps to stop bleeding. However, sometimes clots form inappropriately inside veins and arteries, which can block these blood vessels and cause serious medical problems.
Blood clotting is a complex process that involves many different proteins and other substances in the blood. The main protein involved in clotting is called fibrin. When a blood vessel is injured, fibrinogen (a soluble protein in the plasma) is converted to fibrin by the action of thrombin (a clotting enzyme). Fibrin then forms long strands that entangle red blood cells and other particles in the area of injury, creating a plug (clot) that seals off the wound. This process is aided by platelets (another type of cell in the bloodstream), which help to form an initial seal at the site of injury and also release chemicals that promote clotting.
There are many different disorders that can affect the body’s ability to form clots appropriately. For example, hemophilia is a disorder in which there is deficiency of one of the proteins involved in coagulation, resulting in abnormal bleeding. von Willebrand disease similarly affects platelets, causing increased bleeding. Other disorders can cause increased risk of developing inappropriate clots (thrombosis), such as cancer or certain inherited conditions such as Factor V Leiden mutation or prothrombin gene mutation. In addition, certain medications (including some birth control pills) or medical procedures (such as surgery) can increase the risk of thrombosis.
When a clot forms inside a vein or artery, it can block normal blood flow through these vessels. This can lead to serious medical problems depending on where the clot occurs:
* If a deep vein thrombosis develops in leg veins, it may cause pain and swelling in the affected leg; if untreated, it may lead to pulmonary embolism (PE). PE occurs when part of the clot breaks off and travels through circulation to lodge in arteries supplying lungs, causing difficulty breathing and potentially life-threatening low oxygen levels inblood
* If an arterial thrombosis develops—for example, in coronary arteries supplying heart muscle—it may cause chest pain (angina) or heart attack