Autoimmune Thrombocytopenic Purpura: Signs, Causes, and How to Treat Autoimmune Thrombocytopenic Purpura, also known as ITP, is a condition where the immune system mistakenly attacks and destroys platelets, which are cells that help blood to clot. This can lead to a low platelet count and an increased risk of bleeding. The exact cause of ITP is not fully understood, but it is believed to involve a malfunction in the immune system where it mistakenly targets platelets as foreign invaders ... Immune thrombocytopenia (ITP) is an illness that can lead to bruising and bleeding. Low levels of the cells that help blood clot, also known as platelets, most often cause the bleeding. Immune thrombocytopenia (ITP) is a type of platelet disorder that develops when your blood does not clot as it should because of a low platelet count. When you are injured, platelets (tiny blood cells) stick together to form a plug, called a blood clot, that seals your wound. ITP is a rare autoimmune disorder that lowers your platelet count and increases your risk of bleeding. Learn about the types, causes, symptoms, diagnosis, and treatment options for ITP from Johns Hopkins Medicine.