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Harvard Medical School

Thrombocytopenia

What Is It?

Thrombocytopenia is an abnormally low level of platelets in the blood. Platelets are made by the bone marrow, and help your blood to clot. People with thrombocytopenia can have excessive bleeding.

Most people have more than 150,000 platelets per microliter of blood. Anyone with fewer platelets has some degree of thrombocytopenia. The risk of bleeding increases as the platelet count decreases, so people with less than 10,000 platelets per microliter of blood are at high risk of severe bleeding.

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

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

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

  • A cancer, such as leukemia or lymphoma, gets into the bone marrow and destroys megakaryocytes, the cells that produce platelets.

  • Aplastic anemia affects platelet production.

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

  • Genetic problems, such as Wiskott-Aldrich syndrome or May-Hegglin anomaly, hinder production of normal platelets.

  • Exposure to certain drugs, especially thiazide diuretics or alcohol, slows the production of megakaryocytes. Because drinking large amounts of alcohol can seriously slow platelet production, transient thrombocytopenia is a common syndrome in heavy drinkers, especially if the drinker's diet is low in iron, vitamin B12, or folate.

  • After suffering from a viral infection, such as chicken pox, parvovirus, mumps, rubella or Epstein-Barr virus, 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. Some common causes of this problem include:

  • Immune thrombocytopenic purpura (ITP) — This condition can pass quickly or can last a long time.

  • Autoimmune diseases — These include systemic lupus erythematosus (SLE), polyarteritis and dermatomyositis.

  • AIDS — People with AIDS often develop thrombocytopenia before other symptoms.

  • Complications of pregnancy — About 5% of pregnant women develop mild thrombocytopenia when they are close to delivery.

  • A reaction to a medication — Thrombocytopenia can be caused by any medication, but it occurs somewhat frequently from taking valproic acid (Depakote), gold salts, heparin (Calciparine, Liquaemin), and several other medications. For example, up to 15% of hospitalized patients who receive heparin to prevent blood clots eventually develop thrombocytopenia. In most cases, thrombocytopenia develops within two to five days of starting a new drug.

  • Physical trauma — Platelets can be injured or destroyed as they pass through an artificial heart valve, through a blood vessel graft or through the machines and tubing used in massive blood transfusions or cardiopulmonary bypass surgery.

  • Infections — Thrombocytopenia can develop after such infections as mononucleosis or cytomegalovirus.

  • Thrombotic thrombocytopenic purpura (TTP) — This is a rare disease that causes low levels of platelets, along with a variety of other symptoms and complications.

• Too many platelets remain in the spleen. Normally, about one-third of your platelets are in your spleen and the rest are circulating in your blood. However, if the spleen gets larger because of severe liver disease (especially cirrhosis), Gaucher's disease or cancer, it can begin to hoard too many platelets. This leaves fewer platelets to circulate in your bloodstream, causing thrombocytopenia.