Blood clots

When we bleed, for example with a cut finger, our blood needs to stop flowing so the bleeding stops. The process that stops bleeding is called clotting, or coagulation, and is an important lifesaving process. Platelets, a type of red blood cell fragment, work with plasma proteins (called clotting factors) to stick together over the injury, forming a clot.

A thrombus is a blood clot that forms inside a vessel in the body and stays there. This type of clot (called a thrombus) is dangerous, and can lead to a heart attack or stroke. If thrombi (the plural of thrombus) break loose and move to another part of the body, they are then called emboli (the plural of embolus). The related medical condition where a thrombus has broken free and traveled to lodge in another part of the body is called a thromboembolism.

There are some medical conditions and medicines that can change the blood clot formation process in the body, making blood clots more or less likely.

Types of blood clots treated with anti-clotting medicines

Platelet-based clots

These types of clots occur more often in people with atherosclerosis. In this condition, fatty deposits build up in the arteries (called plaques), and lead to thickening and narrowing of the blood vessel. These blockages can build up enough to block the artery, or if the plaque ruptures a blood clot can form at the place of rupture (or ‘injury’) and block the blood flow in that artery. These blockages can cause a heart attack or stroke. People with atherosclerosis are often given aspirin or another antiplatelet medicine (a type of anti-clotting or antithrombotic medicine) to help treat their condition, or prevent it recurring.

Fibrin-based clots

These clots tend to occur in areas of slow blood flow, when blood pools or collects in one place because it’s not flowing as fast as it should be. This may be in a vein of the leg, for example, after surgery when the person is less active than usual. These clots can also occur in a condition called atrial fibrillation, where the person’s heart beats irregularly and blood may not be pumped through the heart as usual. Anticoagulant medicines, such as warfarin, are the most effective anti-clotting medicine for these types of clots.