Your Guide to ITP: Symptoms, Treatments, and More

How ITP Is Diagnosed: What To Expect

Medically reviewed by Warren Brenner, M.D.

Written by Carrie Madormo, RN, MPH

Posted on August 10, 2026

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Key Takeaways

Immune thrombocytopenia, or ITP, is a rare blood disorder that affects how blood clots, and diagnosing it often requires multiple tests because no single test can confirm the condition on its own.
People with ITP have low platelet levels, which can lead to easy bruising and bleeding, and doctors use a combination of physical exams, blood tests like a complete blood count, and sometimes additional screenings to rule out other causes. Understanding whether someone has primary ITP, where the immune system attacks platelets without a known cause, or secondary ITP, where an underlying condition is responsible, plays an important role in finding the right care.
If you or someone you know is going through the ITP diagnostic process, talking with a hematologist or healthcare provider can help clarify which tests are needed and what the results mean for your overall health and treatment journey.

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If your healthcare team thinks you may have immune thrombocytopenia (ITP) — a rare blood disorder that changes how your blood clots — you’ll likely need several tests to arrive at a diagnosis. Your primary doctor may run the first blood tests. Then they may refer you to a hematologist. This doctor specializes in blood disorders.

In this article, we’ll discuss why an ITP diagnosis may require many tests and what they are. We’ll also cover the differences between primary and secondary ITP.

Why ITP Is a Diagnosis of Exclusion

ITP is considered a diagnosis of exclusion. This means that there isn’t a single test that can confirm the diagnosis. Rather, the healthcare team conducts several tests to rule out other possible causes.

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ITP is a blood disorder that changes how your blood clots. People with ITP have a low level of platelets. Platelets are blood cell fragments that stick together to clot the blood and prevent bleeding. ITP can lead to bleeding and bruising easily.

Several health conditions and disorders can cause low platelets. In people with ITP, the immune system is to blame. The immune system attacks the platelets, clearing them from the blood.

Initial Tests: CBC, Blood Smear, and Basic Workup

To evaluate you for ITP, your healthcare provider will perform a physical exam and ask you several questions about your symptoms. They’ll examine your skin for signs of bleeding.

Possible ITP symptoms include:

Bruises — Pooling of blood under the skin
Petechiae — Tiny red, brown, or purple dots on the skin
Purpura — Larger dots on the skin that form when petechiae blend together
Bleeding gums — Blood or swelling in the gums

Your provider will also perform a medical history. This means they’ll ask you questions about your health history and any recent symptoms. They’ll likely ask you about any new bleeding, such as:

Frequent nosebleeds
Blood in your urine or stool
Heavy menstrual periods

ITP doesn’t always cause symptoms. Some people with low platelet counts don’t have any signs of a bleeding problem.

If you show signs of unusual bleeding, your provider will likely recommend blood tests. These tests can be done in a lab or doctor’s office.

Complete Blood Count

A complete blood count (CBC) is a blood test that measures the number of red blood cells, white blood cells, and platelets in your blood.

People with ITP usually have low platelet counts while their red and white blood cell counts are normal. However, these blood counts may be abnormal if there has been significant bleeding or if you have another medical condition.

A normal platelet level is between 150,000 and 450,000 platelets per microliter of blood. A platelet count below 140,000 is considered low. This condition is called thrombocytopenia.

People with ITP usually have a platelet count below 100,000 platelets per microliter of blood, but the diagnosis depends on more than the platelet count alone.

A CBC test can rule out other causes of low platelets. For example, certain blood cancers such as some leukemias tend to cause low levels of platelets and red blood cells with high levels of white blood cells. Many infections also cause high levels of white blood cells.

Peripheral Blood Smear

When your healthcare provider takes blood for a CBC test, they’ll likely use the sample to run a peripheral blood smear as well. This test involves looking at red blood cells, white blood cells, and platelets under a microscope.

People with ITP have low levels of platelets, and their platelets appear normal under a microscope. Platelets that have an abnormal or irregular shape may be a sign of blood cancer or a different blood disorder.

When Additional Testing or Bone Marrow Examination Is Needed

Some people receive an ITP diagnosis with a physical exam and simple blood test. For others, more invasive tests may be needed. In most cases, a person can begin ITP treatment when their CBC and peripheral blood smear tests suggest ITP.

If treatment isn’t successful, the healthcare team may recommend additional tests to rule out other possible causes of low platelets.

Additional testing may include:

Hepatitis C test — This blood test diagnoses hepatitis C, a long-term liver infection that affects platelet levels and function.
Human immunodeficiency virus (HIV) screening — This blood test diagnoses HIV, which can lower platelet levels.
Helicobacter pylori (H. pylori) test — This test detects a type of bacteria in the digestive tract. H. pylori can cause low platelet levels.
Antinuclear antibody test — This blood test measures antibodies to diagnose lupus. Research shows that 12.8 percent of people with systemic lupus erythematosus (SLE, the most common form of lupus) are diagnosed with primary ITP first.
Direct antiglobulin test (direct Coombs test) — This blood test rules out Evans syndrome, a disorder of breakdown of red blood cells and platelets.
Thyroid function test — This blood test rules out a thyroid disorder, such as hyperthyroidism or hypothyroidism.
Bone marrow examination — This invasive test takes a sample of the bone marrow to diagnose certain cancers. People over age 60 or those who aren’t responding well to ITP treatment may need this test.

Most people with suspected ITP don’t need a bone marrow test. Research shows that this test doesn’t usually change the diagnosis.

A bone marrow test is only considered if the healthcare team suspects cancer or a bone marrow disorder. Signs that a bone marrow test may be needed include an enlarged spleen, lymph node swelling, anemia (low red blood cells), or changes to the white blood cells.

Primary vs. Secondary ITP: Why the Distinction Matters

ITP is a rare condition. In the United States, about 4 in 100,000 children and 3 in 100,000 adults are diagnosed with ITP each year. Once a person is diagnosed with ITP, their healthcare team will work to determine which type of ITP they have.

About 80 percent of people with ITP have primary ITP. In primary ITP, the immune system mistakenly attacks platelets even though there is no other known condition causing it. Because the immune system attacks the body’s own cells, primary ITP is considered an autoimmune disorder.

Secondary ITP causes low platelets because of an underlying condition. Certain autoimmune conditions, infections, and blood cancers can lead to secondary ITP.

It’s important to know which type of ITP you have to determine the most effective treatment plan. People with secondary ITP need to have their underlying condition treated to correct their platelet counts.

ITP is also classified by how long the condition has been going on:

Acute (newly diagnosed) ITP — Less than three months
Persistent ITP — Between three and 12 months
Chronic ITP — More than 12 months

Getting an ITP diagnosis can take time because no single test can confirm the condition. Your healthcare team will review your symptoms, medical history, and blood test results while ruling out other causes of low platelets.

Once they confirm the diagnosis and determine the type of ITP, they can recommend the treatment and follow-up care that best fit your needs.