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Causes
By Mayo Clinic staffThe exact cause of ITP isn't known. That's why it's referred to as idiopathic, which means "of unknown cause." It is known, however, that in people with idiopathic thrombocytopenic purpura, the immune system malfunctions and begins attacking platelets as if they were foreign substances.
Antibodies produced by your 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 normal.
Ordinarily, you have anywhere from 150,000 to 450,000 platelets per microliter of circulating blood. Adults and children with ITP often have platelet counts below 20,000. As the number of platelets decreases, your risk of bleeding increases. The greatest risk is when your platelet count falls very low — below 10,000 platelets per microliter. At this point, internal bleeding may occur despite a lack of any injury.
In most children with ITP, the disorder follows a viral illness, such as the mumps or the flu. It may be that an infection sets off the immune system, triggering it to malfunction.
- Idiopathic thrombocytopenic purpura (ITP). The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec11/ch133/ch133d.html. Accessed Aug. 28, 2010.
- Diz-Kucukkaya R, et al. Thrombocytopenia. In: Lichtman MA, et al. Williams Hematology. 8th ed. New York, N.Y.: McGraw-Hill Companies, Inc.; 2010. http://www.accessmedicine.com/content.aspx?aID=6238643. Accessed Aug. 28, 2010.
- What is idiopathic thrombocytopenic purpura? National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/Itp/ITP_All.html. Accessed Aug. 27, 2010.
- George JN. Treatment and prognosis of immune (idiopathic) thrombocytopenic purpura in adults. http://www.uptodate.com/home/index.html. Accessed Aug. 27, 2010.
- Blanchette V, et al. Childhood immune thrombocytopenic purpura: Diagnosis and management. Hematology/Oncology Clinics of North America. 2010;24:249.
- Bussel JB. Traditional and new approaches to the management of immune thrombocytopenia: Issues of when and who to treat. Hematology/Oncology Clinics of North America. 2009;23:1329.
- Anderson CF (expert opinion). Mayo Clinic, Rochester, Minn. Aug. 29, 2010.
- Nplate (prescribing information). Thousand Oaks, Calif.: Amgen; 2008. http://www.nplate.com/patient/pdf/nplate_pi.pdf. Accessed Sept. 7, 2010.
- Promacta (prescribing information). Research Triangle Park, N.C.: Glaxo SmithKline; 2010. http://us.gsk.com/products/assets/us_promacta.pdf. Accessed Sept. 7, 2010.
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