Diagnosis

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

Samples of your blood will be checked for:

• The number of platelets
• The size of your platelets
• Specific genetic flaws, such as the JAK2, CALR or MPL gene mutation
• Iron levels
• Markers of inflammation

Bone marrow tests

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.