Tests and diagnosis

By Mayo Clinic Staff

Blood tests that can help confirm a diagnosis of essential thrombocythemia include:

  • Complete blood count (CBC). This test determines the number of platelets in your blood.
  • Blood smear. A small amount of your blood is examined under a microscope to view the condition of your platelets, such as whether they're abnormally large or clumped together.
  • Genetic testing. Special tests can determine whether you have chromosomal abnormalities that can cause a high platelet count and whether you have a JAK2 gene mutation.
  • Other blood tests. Your doctor may check the level of iron in your blood or test for markers of inflammation.

If your blood count is above 450,000 platelets per microliter of blood, your doctor will look for an underlying condition. If there's no evident cause of your high platelet count, and it remains high over time, your doctor may suggest a bone marrow test. The two types of bone marrow tests 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 essential thrombocythemia, your bone marrow has a higher than normal number of the large cells that make platelets (megakaryocytes).
Sept. 22, 2012

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