ITP, or immune thrombocytopenic purpura and also called immune thrombocytopenia, is a condition in which the blood has a lower number of platelets than normal. Platelets are cells that help the blood clot.1 ITP is called an autoimmune disease2 since it is the result of the body's immune system attacking platelets as if they are foreign cells.3
In ITP, there are two reasons that platelet counts are lower than normal:
1. Healthy platelets are destroyed.2,4
2. The body doesn't produce enough platelets to make up for those that have been destroyed.2,4-6
Here's what happens:
|The two factors involved in ITP
|Increased platelet destruction
||Decreased platelet production
|Antibodies made by the body's immune system attack healthy platelets. The spleen, an organ that is part of the immune system, then destroys these platelets.2
||Platelet production is inadequate because antibodies damage platelet-producing cells in the bone marrow. In addition, levels of a protein in the body called thrombopoietin, or TPO, are too low.2,4-8
(See Facts about platelets and ITP below for more details.)
It is not known what causes the body to act this way. For that reason, ITP is also referred to as idiopathic thrombocytopenic purpura. Idiopathic means the cause is unknown. Purpura means bleeding in the skin (for example, bruising) or mucous membranes, which can occur in people with ITP.7
When there are fewer platelets than normal, broken blood vessels under the skin (called petechiae) or bruising may be visible.7 However, some people with ITP have no obvious symptoms.8
One of the biggest concerns for people with ITP is uncontrolled bleeding, which can be either external such as bleeding because of an injury, or internal such as a hemorrhage in the brain. Sometimes uncontrolled bleeding can be spontaneous, meaning the bleeding can arise without an event or injury occurring.9 The seriousness of uncontrolled bleeding makes ITP a complex condition that should be appropriately managed.
Facts about platelets and ITP
The more you know about ITP, the more prepared you will be to participate in your treatment plan.
- Platelets are small disk-shaped cells that bind together to form a plug in order to seal the blood vessel and stop bleeding.1,10
- Platelets are made by specialized cells in the bone marrow called megakaryocytes.10
- A healthy platelet lasts for about 9 or 10 days in the blood, but in someone with ITP, the immune system removes and destroys platelets much sooner, maybe in as soon as a few hours after they enter circulation.6
- The immune system sends antibodies to attack platelets and damage megakaryocytes—the cells that make platelets.2,6
- TPO, a protein made by the liver, controls the production of platelets.11
- When the body functions normally, too few platelets in the bloodstream cause more TPO to be sent to bone marrow cells—boosting platelet production.11 For people with ITP, the TPO level is too low relative to the level of platelets. Less TPO in the bone marrow means that fewer platelets are produced and platelet levels stay low.4,5
In short, in ITP, antibodies destroy platelets and interfere with the production of new platelets that could replace them. Since the levels of TPO are lower than they should be, the bone marrow does not get a sufficient signal to make adequate levels of platelets.2,4,6
- MedlinePlus Medical Encyclopedia. Idiopathic thrombocytopenic purpura (ITP). http://www.nlm.nih.gov/medlineplus/ency/article/000535.htm. Accessed December 16, 2010.
- Houwerzijl EJ, Blom NR, van der Want JJL, et al. Ultrastructural study shows morphologic features of apoptosis and para-apoptosis in megakaryocytes from patients with idiopathic thrombocytopenic purpura. Blood. 2004;103:500-506.
- Mayo Clinic. Idiopathic thrombocytopenic purpura (ITP). http://www.mayoclinic.com/health/ idiopathic-thrombocytopenic-purpura/DS00844/METH. Accessed January 6, 2011.
- Nichol JL. Endogenous TPO (eTPO) levels in health and disease: possible clues for therapeutic intervention. Stem Cells. 1998;16(suppl 2):165-175.
- Emmons RV, Reid DM, Cohen RL, et al. Human thrombopoietin levels are high when thrombocytopenia is due to megakaryocyte deficiency and low when due to increased platelet destruction. Blood. 1996;87(10):4068-4071.
- Gernsheimer T. Pathophysiology and thrombokinetics in autoimmune thrombocytopenia. Blood Rev. 2002;16:7-8.
- National Heart Lung and Blood Institute Diseases and Conditions Index. Idiopathic thrombocytopenic purpura. http://www.nhlbi.nih.gov/health/dci/Diseases/Itp/ITP_WhatIs.html Accessed December 14, 2010.
- George JN, Woolf SH, Raskob GE, et al. Idiopathic thrombocytopenic purpura: a practice guideline developed by explicit methods for the American Society of Hematology. Blood. 1996;88(1):3-40.
- Merck Manual Home Edition. Thrombocytopenia (ITP, TTP). http://www.merck.com/mmhe/ sec14/ch173/ch173d.html?qt=ITP&alt=sh. Accessed November 1, 2010.
- McNicol A, Israels SJ. Platelets and anti-platelet therapy. J Pharmacol Sci. 2003;93:381-396.
- Kaushansky K. The molecular mechanisms that control thrombopoiesis. J Clin Invest. 2005;115(12):3339-3347.