Thrombosis is the formation of a blood clot (thrombus) inside a vessel that partially or completely blocks blood flow. Blood clotting is vital for stopping bleeding, but when a clot forms where it should not, it becomes dangerous.
In arteries, thrombosis usually develops on an atherosclerotic plaque and leads to a heart attack or stroke; in veins, it leads to deep vein thrombosis.
What thrombosis is
A thrombus is a clot made of platelets, fibrin and blood cells. Normally it seals a damaged vessel and dissolves once healing is complete. In thrombosis the clot forms in excess or fails to dissolve, disrupting the blood supply to the organ downstream of the blockage.
Arterial and venous thrombosis
Arterial thrombosis more often forms on a ruptured atherosclerotic plaque and causes acute catastrophes — myocardial infarction, ischemic stroke, acute limb ischemia. Venous thrombosis is primarily deep vein thrombosis of the legs (DVT). Its dangerous complication is pulmonary embolism (PE), when a broken-off clot blocks the pulmonary vessels.
Risk factors: Virchow's triad
Classically, the risk of thrombosis is described by Virchow's triad: slowed blood flow (stasis), damage to the vessel wall and increased blood clotting. In practice these are prolonged immobility (bed rest, long flights), surgery and trauma, cancer, pregnancy and childbirth, estrogen use, smoking, obesity, atrial fibrillation and inherited thrombophilias.
Symptoms and prevention
Deep vein thrombosis shows up as swelling, pain, and warm, reddened skin of one leg. Signs of PE — sudden shortness of breath, chest pain, rapid breathing — require emergency care. Prevention: moving and stretching during long periods of sitting, quitting smoking, weight control, compression stockings, and anticoagulants in high-risk patients.
Calculate using this marker
Calculators where Thrombosis is used directly:
Frequently asked questions
How is thrombosis different from thromboembolism?
Thrombosis is the formation of a clot in place, inside a specific vessel. Thromboembolism is when a clot (or part of it) breaks off, travels with the bloodstream and blocks a vessel elsewhere — for example, PE, where a clot from the leg veins blocks the pulmonary artery.
Which test shows thrombosis?
The screening marker is D-dimer: a rise indicates active formation and breakdown of clots, but it is non-specific. Thrombosis is confirmed with imaging: vein ultrasound for DVT, CT angiography for PE. A doctor interprets the results.