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What Is It?

Thrombocytopenia is an abnormally low level of platelets in the blood.

Platelets are made by the bone marrow. They help your blood to clot. People with thrombocytopenia can have excessive bleeding.

This condition can occur in varying degrees. The risk of bleeding increases as the platelet count decreases.

Thrombocytopenia can occur alone. Or, it can develop as a complication of another disease, such as cancer or a viral infection. In some cases, it is a chronic (long-lasting) condition that persists for years. In other cases, it develops suddenly and dramatically.

In general, thrombocytopenia develops for one or more of the following reasons:

  • The body's bone marrow fails to produce enough platelets. This can happen because:

    • A cancer gets into the bone marrow and destroys megakaryocytes. These are the cells that produce platelets.

    • Aplastic anemia affects platelet production.

    • A toxic chemical, radiation therapy or chemotherapy destroys megakaryocytes.

    • Genetic problems hinder production of normal platelets.

    • Exposure to certain drugs or alcohol slows the production of megakaryocytes. Thrombocytopenia is common in heavy drinkers.

    • After suffering from a viral infection, some patients will have decreased platelet production. This problem is usually short term and improves without treatment.

  • The bone marrow produces enough platelets, but the body destroys them. The immune system can produce antibodies that attack platelets. Some causes of this problem include:

    • Immune thrombocytopenic purpura (ITP). This condition can pass quickly or can last a long time. ITP can occur by itself or it can be associated with other autoimmune disorders, such as systemic lupus erythematosus (SLE)

    • HIV infection. People infected with the virus sometimes develop low platelet counts.

    • A complication of pregnancy. A small percentage of pregnant women develop a mild form of this condition when they are close to delivery.

    • A reaction to a medication. Thrombocytopenia can be caused by any medication. For example, heparin, quinine and valproic example (Depakote) can trigger the immune system to make anti-platelet antibodies. In most cases, the condition develops within days of starting a new drug.

    • Physical trauma. Platelets can be injured or destroyed as they pass through:

      • An artificial heart valve

      • A blood vessel graft

      • Machines and tubing used in massive blood transfusions or cardiopulmonary bypass surgery

    • Infections. The condition can develop after such infections as mononucleosis or cytomegalovirus.

    • Thrombotic thrombocytopenic purpura (TTP). This is a rare disease. Blood clots form in the smallest arteries throughout the body. Platelets are consumed by this process. People with TTP also have anemia (low red blood cell count), fever, kidney malfunction and neurological symptoms.

  • Too many platelets remain in the spleen. Normally, about one-third of your platelets are in your spleen. The rest are circulating in your blood. However, if the spleen gets larger because of severe liver disease, it can begin to hoard too many platelets. This leaves fewer platelets to circulate in your bloodstream.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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