In most cases, an autoimmune response is thought to cause immune thrombocytopenia (ITP).
Normally, your immune system helps your body fight off infections and diseases. In ITP, however, your immune system attacks and destroys your body's platelets by mistake. Why this happens isn't known.
In some people, ITP may be linked to viral or bacterial infections, such as HIV, hepatitis C, or H. pylori.
Children who have acute (short-term) ITP often have had recent viral infections. These infections may "trigger" or set off the immune reaction that leads to ITP.