Thrombocythemia

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Tests and diagnosis

By Mayo Clinic staff

You may find out you have thrombocythemia through a routine blood test that shows you have a higher than normal platelet count. Or, if you've had an unexpected blood clot or bleeding episode, or your doctor finds that your spleen is enlarged, your doctor may order a complete blood count (CBC) to determine your platelet count. A blood smear — a test in which a small amount of your blood is examined under a microscope — helps determine the condition of your platelets. Other blood tests can determine whether you have genetic factors that can cause a high platelet count.

If your blood count is above 600,000 platelets per microliter of blood, then your doctor will look for an underlying condition. If there's no evident cause of your high platelet count, and if your platelet count remains high over time, then your doctor may request a bone marrow test. There are two types of bone marrow tests, which provide different but complementary information about your blood cells. Often, they're done together.

  • Bone marrow aspiration. Your doctor extracts a small amount of your liquid bone marrow through a needle and examines it under a microscope, looking for abnormal cells.
  • Bone marrow biopsy. Your doctor takes a sample of solid bone marrow tissue through a needle for examination under a microscope. If you have thrombocythemia, your bone marrow has more than a normal amount of the large cells that make platelets.

DS01087

July 16, 2008

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