In some people thrombocytopenia is caused by the immune system mistakenly attacking and destroying platelets. If the cause of this immune reaction is unknown, the condition is called idiopathic thrombocytopenic purpura. Idiopathic means "of unknown cause."
In most children with ITP, the disorder follows a viral illness, such as the mumps or the flu. It may be that the infection triggers the immune system malfunction.
Increased breakdown of platelets
In people with ITP, antibodies produced by the immune system attach themselves to the platelets, marking the platelets for destruction. The spleen, which helps your body fight infection, recognizes the antibodies and removes the platelets from your system. The result of this case of mistaken identity is a lower number of circulating platelets than is normal.
A normal platelet count is generally between 150,000 and 450,000 platelets per microliter of circulating blood. People with ITP often have platelet counts below 20,000. Because platelets help the blood clot, as their number decreases, your risk of bleeding increases. The greatest risk is when your platelet count falls very low â below 10,000 platelets per microliter. At this point, internal bleeding may occur even without any injury.