Tests and diagnosis

By Mayo Clinic Staff

If your blood count is above 450,000 platelets per microliter of blood, your doctor will look for an underlying condition. He or she will rule out all other causes of high platelet counts to confirm a diagnosis of essential thrombocythemia. Blood tests may include:

  • Complete blood count. 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 size and activity of your platelets.
  • Genetic testing. Special tests can determine whether you have chromosomal abnormalities that can cause a high platelet count and whether you have a JAK2, CALR or MPL gene mutation.
  • Other blood tests. Your doctor may check the level of iron in your blood or test for markers of inflammation.

Your doctor may also suggest two bone marrow tests:

  • Bone marrow aspiration. Your doctor extracts a small amount of your liquid bone marrow through a needle. The sample is examined under a microscope for abnormal cells.
  • Bone marrow biopsy. Your doctor takes a sample of solid bone marrow tissue through a needle. The sample is examined under a microscope to determine whether your bone marrow has a higher than normal number of the large cells that make platelets (megakaryocytes).
June 24, 2015