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Overview of Thrombocytopenia

By David J. Kuter, MD, DPhil, Harvard Medical School;Massachusetts General Hospital Cancer Center

Thrombocytopenia is a deficiency of platelets (thrombocytes), which increases the risk of bleeding.

  • Thrombocytopenia occurs when the bone marrow makes too few platelets or when too many platelets are destroyed or accumulate within an enlarged spleen.

  • Bleeding in the skin and bruising occur.

  • Blood tests are used to make the diagnosis and determine the cause.

  • Sometimes treatment (such as platelet transfusion, prednisone, or removal of the spleen) is needed.

Platelets are cell fragments that circulate in the bloodstream and help blood clot. The blood usually contains about 140,000 to 440,000 platelets per microliter. When the platelet count falls below about 50,000 platelets per microliter of blood, bleeding can occur even after relatively minor injury. The most serious risk of bleeding, however, generally does not occur until the platelet count falls below 10,000 to 20,000 platelets per microliter of blood. At these very low levels, bleeding may occur without any recognized injury. See also Overview of Platelet Disorders.

Causes

Many disorders can cause thrombocytopenia.

Thrombocytopenia can occur when the bone marrow does not produce enough platelets, as happens in leukemia and some anemias.

Infection with hepatitis C virus, the human immunodeficiency virus (HIV, the virus that causes AIDS), Epstein-Barr virus (the usual cause of mononucleosis), and many other viruses may result in thrombocytopenia.

Platelets can become entrapped in an enlarged spleen, as happens in cirrhosis of the liver, myelofibrosis, and Gaucher disease, reducing the number of platelets in the bloodstream.

Massive blood transfusions can dilute the concentration of platelets in the blood.

Some drugs can also cause thrombocytopenia.

Finally, the body may use or destroy too many platelets, as occurs in many disorders, three of the most notable being immune thrombocytopenia, thrombotic thrombocytopenic purpura, and hemolytic-uremic syndrome.

Symptoms and Complications

Bleeding in the skin may be the first sign of a low platelet count. Many tiny red dots (petechiae) often appear in the skin on the lower legs, and minor injuries may cause bruises (ecchymoses). The gums may bleed, and blood may appear in the stool or urine. Menstrual periods may be unusually heavy. Bleeding may be hard to stop.

Bleeding worsens as the number of platelets decreases. People who have very few platelets may lose large amounts of blood into the digestive tract or may develop life-threatening bleeding in the brain even though they have not been injured.

The rate at which symptoms develop can vary depending on the cause of thrombocytopenia.

Diagnosis

  • Blood tests to measure platelet count

Doctors suspect thrombocytopenia in people who have abnormal bruising and bleeding. They often check the number of platelets routinely in people who have disorders that cause thrombocytopenia. Sometimes they discover thrombocytopenia incidentally when blood tests are done for other reasons in people who have no bruising or bleeding.

Determining the cause of thrombocytopenia is critical to treating the condition. Certain symptoms may help determine the cause. For example, people usually have a fever when thrombocytopenia results from an infection. In contrast, they usually do not have a fever when the cause is ITP, TTP, or HUS. An enlarged spleen, which a doctor may be able to feel during a physical examination, suggests that the spleen is trapping platelets and that thrombocytopenia results from a disorder that causes the spleen to enlarge.

The platelet count may be measured with an automated counter to determine the severity of thrombocytopenia, and a sample of blood may be examined under a microscope to provide clues to its cause. A sample of bone marrow removed and examined under a microscope ( bone marrow biopsy and aspiration) may occasionally be needed to provide information about platelet production.

Treatment

  • Avoidance of injury and drugs that affect platelets

  • Sometimes platelet transfusion

People with a low platelet count and abnormal bleeding usually should not take drugs that impair platelet function (such as aspirin). People who have a very low platelet count are often treated in a hospital. When bleeding is severe, platelets may be transfused, although sometimes the transfused platelets also are destroyed by the underlying disorder.

Treating the cause can often treat the thrombocytopenia. Thrombocytopenia caused by a drug usually is corrected by stopping the drug.

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