Idiopathic thrombocytopenic purpura is a bleeding disorder in which the immune system destroys platelets, which are necessary for normal blood clotting. Persons with the disease have too few platelets in the blood.

ITP is sometimes called immune thrombocytopenic purpura.

ITP occurs when certain immune system cells produce antibodies against platelets. Platelets help your blood clot by clumping together to plug small holes in damaged blood vessels.

The antibodies attach to the platelets. The spleen destroys the platelets that carry the antibodies.

In children, the disease sometimes follows a viral infection. In adults, it is more often a chronic (long-term) disease and can occur after a viral infection, use of certain drugs, pregnancy, or an immune disorder.

ITP affects women more frequently than men, and is more common in children than adults. The disease affects boys and girls equally.