Description

Thrombocytopenia (thrombocythemia) is a blood disorder characterized by an abnormally low number of circulating platelets (thrombocytes) in the bloodstream. Because platelets play an important role in the process of coagulation (blood clotting) and in the plugging of damaged blood vessels, persons with decreased platelets bruise easily and can have episodes of excessive bleeding (hemorrhage). Thrombocytopenia is usually an acquired disorder, but it can also be congenital, as in neonatal rubella (German measles).

Platelets are irregular, disc-shaped fragments of large cells called megakaryocytes, which are found in the spongy center of long bones (bone marrow). They are the smallest cell-like structures in the blood. When a blood vessel is punctured or damaged, normal mature platelets have a tendency to aggregate (group) together at...