Thrombus

Thrombus
Other names	Blood clot
Diagram of a thrombus (blood clot) that has blocked a vein valve
Specialty	Vascular surgery
Symptoms	abrupt change in mental status, chest pain, cramp-like feeling, fatigue, passing out (syncope), and swelling in the arm and/or leg
Complications	bleeding risks from taking anticoagulants, breathing problems, heart attacks, stroke
Duration	c. 3–6 months
Types	Superficial thrombophlebiti and Thrombophlebitis migrans
Causes	injury to the artery, sepsis or viral infection, immobility
Risk factors	hospitalization, immobility, obesity, pregnancy, physical trauma
Diagnostic method	magnetic resonance angiography, ultrasound, and venography
Prevention	smoking cessation, regular exercise, improved blood flow, management of comorbidities
Treatment	Anticoagulants: edoxaban, tinzaparin, unfractionated heparin
Medication	apixaban, edoxaban, and rivaroxaban
Deaths	100,000–300,000 each year

A thrombus (pl.: thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cross-linked fibrin protein. The substance making up a thrombus is sometimes called cruor. A thrombus is a healthy response to injury intended to stop and prevent further bleeding, but can be harmful in thrombosis, when a clot obstructs blood flow through healthy blood vessels in the circulatory system.

In the microcirculation consisting of the very small and smallest blood vessels the capillaries, tiny thrombi known as microclots can obstruct the flow of blood in the capillaries. This can cause a number of problems particularly affecting the alveoli in the lungs of the respiratory system resulting from reduced oxygen supply. Microclots have been found to be a characteristic feature in severe cases of COVID-19 and in long COVID.^[1]

Mural thrombi are thrombi that adhere to the wall of a large blood vessel or heart chamber.^[2] They are most commonly found in the aorta, the largest artery in the body, more often in the descending aorta, and less often in the aortic arch or abdominal aorta.^[2] They can restrict blood flow but usually do not block it entirely. They appear grey-red along with alternating light and dark lines (known as lines of Zahn) which represent bands of white blood cells and red blood cells (darker) entrapped in layers of fibrin.^[3]