Platelets (thrombocytes) are small pieces of cells that play an important role in blood clotting by clumping and forming plugs when necessary. Thrombocytopenia (throm-boe-sie-toe-PEE-nee-uh) is a condition in which blood doesn't clot properly because there aren't enough platelets.

Causes of thrombocytopenia include increased breakdown and destruction of platelets (related to a problem with the immune system), reduced production of platelets or trapping of platelets in the spleen.

Thrombocytopenia can occur as a result of another condition or disorder, such as disseminated intravascular coagulation or DIC (blood clotting problem), leukemia, lymphoma, bone marrow failure (aplastic anemia), an immune system problem, some viruses or certain genetic conditions. It can also occur from sepsis, which is a potentially life-threatening complication of an infection, or as a medication side effect or from exposure to certain toxic chemicals.

The most common reason for thrombocytopenia in children is idiopathic thrombocytopenic purpura (ITP), also called immune system thrombocytopenia. Idiopathic means unknown cause.

ITP occurs when the immune system mistakenly attacks and destroys platelets. Recent viral infections can lead to short-term ITP in children. If ITP in children lasts longer than six months, it's known as chronic ITP.

May 29, 2014