Overview
Thrombosis is the formation of a blood clot (thrombus) within a blood vessel that partially or completely obstructs blood flow. Clotting is a normal protective response after injury, involving platelets and fibrin, but when it occurs inappropriately inside intact vessels it can impair tissue perfusion and cause organ damage. The term derives from Greek roots: θρόμβος (thrombos, “clot”) and θρόμβωσις (thrombosis).
Causes and risk factors
Thrombus formation typically results from a combination of abnormalities in the vessel wall, blood flow, and blood composition. Common contributing factors include endothelial injury (from trauma or inflammation), reduced or turbulent blood flow, and increased coagulability. Risk factors often cited are prolonged immobility, surgery, certain cancers, pregnancy, hormonal therapies, inherited clotting disorders, smoking, obesity, and older age. Medications and acute illness can also alter clotting tendencies.
Types and typical locations
Thromboses are commonly categorized by location and vessel type. Venous thrombosis most often affects deep veins of the legs (deep vein thrombosis, DVT) and may travel to the lungs as a pulmonary embolism. Arterial thrombosis can obstruct arteries supplying the heart, brain, or limbs, producing heart attack, ischemic stroke, or critical limb ischemia. Thrombi may also form in the heart chambers, on prosthetic valves, or in unusual sites such as cerebral venous sinuses.
Signs, complications and distinctions
Symptoms vary by site: DVT can cause limb swelling, pain and warmth; pulmonary embolism often produces shortness of breath and chest pain; arterial occlusion may present with sudden loss of function or severe pain. A key distinction is embolism: a piece of thrombus that detaches and travels can lodge downstream, causing acute ischemia. Prompt recognition is important because complications can be life-threatening.
Diagnosis, treatment and prevention
Diagnosis combines clinical assessment with imaging and laboratory tests. Ultrasound is commonly used for peripheral veins, while CT or MRI-based techniques are applied for chest, brain or abdominal vessels. Treatment aims to stop clot growth, prevent embolization and reduce recurrence. Options include anticoagulant drugs, clot-dissolving (thrombolytic) therapy in selected cases, and mechanical removal in specialized settings. Supportive measures and risk reduction—mobility after surgery, compression garments, and addressing modifiable risks—are central to prevention.
Further reading and resources
For introductory information about clotting and circulation see basic circulatory system resources. Clinical guidelines and patient information on diagnosis and management are available through medical organizations and health services; a helpful overview for patients is available at patient-focused thrombosis information. Professional references explaining imaging and treatment options can be consulted at clinical reference sources.
Notable fact: while clotting protects against bleeding, the same mechanisms can become harmful when regulation is lost, making thrombosis a major focus of preventive and acute medical care.