Those with ITP have a lower platelet count. It can range from severe cases that hover close to zero to more mild cases where the counts stay in closer to 100,000. 30,000 is often considered a 'safe' count', one that is high enough to protect against cerebral hemorrhage. In people with ITP the platelets are often enlarged. They stay in the blood stream from a few hours to close to the normal eight to ten days depending on the severity of the disease.
Platelets play a crucial part in the blood clotting process by forming a platelet plug.
This is a two step process. Activation can be stimulated by components released when the blood vessel is damaged and by thrombin, released during the blood clotting process. When platelets become activated they change. They release agents which recruit and activate the surrounding platelets. The result of these two processes is the formation of fibrin which stabilizes the platelet plug, stops bleeding and allows injuries to heal.