How Is ITP Diagnosed?

Getting an answer can take a while with immune thrombocytopenia (ITP), and that wait can be frustrating. There is no single test that proves you have ITP. Instead, your doctor determines a diagnosis based on exploring and eliminating other possible causes of a low platelet count. This is known as a diagnosis of exclusion.^1-4

Your doctor will review your medical history, examine you, and order tests to look for other reasons your platelets could be low, such as another illness or a drug you take. ITP is usually diagnosed only after those other possibilities are eliminated.^1-4

Your platelet count and what the numbers mean

A normal platelet count is between 150,000 and 450,000 per microliter of blood. If your count is lower than 100,000 per microliter and there is no other reason for it, you are considered to have ITP.³

Your number matters, but it is not the whole story. In general, the lower your count, the more symptoms you may have, though this differs a lot from person to person.³

Blood tests

There are a few common blood tests that doctors use to learn more about your health and what is happening in your body. These tests could include:^3,4,6

• Complete blood count (CBC) – Measures the cells in your blood, including your platelets. In ITP, the platelet count is low while the rest of the results are usually normal.
• Blood smear – A sample of your blood is examined under a microscope so your platelets can be looked at directly.
• Tests for other conditions – If you have risk factors, you may be screened for HIV, hepatitis C, or an H. pylori infection, because each can cause a low platelet count.

When a bone marrow test is used

A bone marrow test can be part of the workup. In adults, a bone marrow biopsy is rarely needed, and it is used to rule out other conditions rather than to confirm ITP. If your doctor suggests one, ask what they are looking for and how the result would change your plan.^1,4

How long you have had it matters, too

Part of the picture is time. Doctors describe ITP by how long it lasts: acute ITP goes away within 3 months, persistent ITP lasts 3 to 12 months, and chronic ITP lasts longer than 12 months. In adults, ITP is usually persistent or chronic.^3,5,6
This is why your first visit is not the end of the process. Your team will keep checking your counts over time.

What your results mean for treatment

A diagnosis does not automatically mean you start treatment. Guidance from the American Society of Hematology says that adults with newly diagnosed ITP who have a platelet count of 30,000 per microliter or higher, and no bleeding or only minor bleeding – such as minor bruising or nosebleeds – can be observed rather than treated. Treatment with corticosteroids is recommended when the count is below that level.^1,7

Treatment decisions should be based on your symptoms, not on your platelet count alone. Mild bruising with no other symptoms may call for watching and waiting. This is a shared decision between you and your doctor, and it works best with open, two-way communication.^1,3,7

Talking with your doctor

Ask what your platelet count was, what it was the last time, and what number would change your plan. Ask which other conditions were ruled out and how. Ask how often your counts will be checked from here.

If you feel unsure, it is reasonable to ask about seeing a hematologist, a doctor who specializes in blood disorders. Getting clear answers is part of your care.