Platelets (thrombocytes) are small, disc-shaped, cell fragments derived from stem cells in the bone marrow). They account for less than 1% of the cellular components within blood.2, 20
Platelets form mechanical plugs in response to blood vessel injury.17 Glycoproteins on the surface of platelets enable adhesion to vessel walls and attachment of von Willebrand factor. Together, these actions help groups of platelets clump and form the mechanical plug.17 Platelets also produce molecules that promote coagulation and healing of injured blood vessels, including fibrinogen, fibronectin, von Willebrand factor and vitronectin. 2, 17, 20, 21
The coagulation cascade animation shows how platelets are involved in coagulation in healthy individuals.
Inherited platelet dysfunction
Inherited platelet dysfunction may be intrinsic (i.e. due to a problem with the platelets themselves) or extrinsic (i.e. due to an external factor essential to their function). Examples of platelet dysfunctions include:
Acquired platelet dysfunction
- Defects in glycoproteins on the platelet surface (intrinsic), responsible for syndromes in which platelets do not aggregate, or cannot adhere to the vessel wall. In both cases, the platelet plug cannot form22
- Storage pool disease, an intrinsic dysfunction found mainly in women. Adequate levels of the molecules normally produced by platelets cannot be stored and platelet function is impaired22
- Von Willebrand disease (VWD), an extrinsic platelet dysfunction, and the most common inherited bleeding disorder. VWD is caused by a deficiency or abnormality of von Willebrand factor, which is essential for platelet adhesion to the vessel wall and platelet aggregation.23
Some drugs inhibit the normal functioning of platelets and increase the risk of bleeding. These drugs include nonsteroidal anti-inflammatory agents (NSAIDS), antiplatetelet therapy, such as aspirin or clopidogrel, and beta-lactam antibiotics such as penicillin (at high doses).
Low levels of platelets in blood (thrombocytopenia) can be caused by reduced platelet production or increased platelet destruction.22
Reduced platelet production can be caused by deficiency in vitamin B12 or folate as well as chemotherapy.22 Increased platelet destruction can be due to the production of antiplatelet antibodies and subsequent destruction by the immune system . This occurs in leukemia and lymphoma. Viral infections (e.g. HIV) have also been associated with the presence of antiplatelet antibodies . Bacterial infection of the blood accelerates platelet destruction, sometimes causing severe thrombocytopenia.
10/28/2014 11:54 AM