what is a blood clot
1 A blood clot is a mass formed by platelets and fibrin in the blood to stop bleeding. 2  There are a variety of risk factors and illness that can lead to blood clot formation. 3  Causes of blood clots may include: 4  certain heart conditions,5  pregnancy, 6  prolonged immobility, 7  smoking, 8  certain medications, 9  surgery, and. A blood clot is a mass formed by platelets and fibrin in the blood to stop bleeding. 2  There are a variety of risk factors and illness that can lead to blood clot formation. 3  Causes of blood clots may include: 4  certain heart conditions,