Arm thrombosis. Coloured X-ray angiogram of a thrombus (blood clot, yellow/green, upper centre) in an artery (dark blue) in an arm. The upper arm bone (the humerus) runs from top centre to bottom right. The artery runs from top left to bottom centre, and the thrombus is seen at the point where it passes in front of the bone. A severe thrombus may cut off the supply of blood to parts of the body, or it may detach and travel to the heart or lungs where it may cause death. A thrombus can arise in diseased arteries, and can be treated with clot-dissolving drugs. X-ray angiography injects a radio-opaque contrast medium to highlight blood vessels on an X-ray.