How Is Idiopathic Thrombocytopenic Purpura Diagnosed?

Your doctor will diagnose idiopathic thrombocytopenic purpura (ITP) based on your medical history, a physical exam, and test results.

Your doctor will want to make sure that your low platelet count isn't due to another condition (such as an infection) or a side effect of medicines you're taking (such as chemotherapy medicines or aspirin).

Medical History

Your doctor may ask about:

• Your signs and symptoms of bleeding and any other signs or symptoms you're having
• Whether you have illnesses that could lower your platelet count or cause bleeding
• Medicines or any other over-the-counter supplements or remedies you take that could cause bleeding or lower your platelet count

Physical Exam

Your doctor will give you a physical exam and look for signs of bleeding and infection. For example, your doctor may look for pinpoint red spots on the skin and bruising or purplish areas on the skin or mucous membranes. These are signs of bleeding under the skin.

Diagnostic Tests

You'll likely have blood tests to check your platelets. These tests usually include:

• A complete blood count. This test shows the numbers of different kinds of blood cells, including platelets, in a small sample of your blood. In ITP, the red and white blood cell counts are normal.
• A blood smear. During this test, some of your blood is put on a slide. A microscope is then used to look at your platelets and other blood cells. In ITP, the number of platelets is lower than normal.

You also may have a blood test to check for the antibodies that attack platelets.

If blood tests show that you have a low number of platelets, your doctor may recommend more tests to confirm a diagnosis of ITP. For example, bone marrow tests may be used to see whether your bone marrow is making platelets.

Some people who have mild ITP have few or no signs of bleeding. These people may be diagnosed only after a blood test done for another reason shows that they have a low platelet count.