How is Essential Thrombocythemia Diagnosed?

Essential Thrombocythemia (ET) is a rare blood disorder, and diagnosing it involves more than just spotting a high platelet count. Because many conditions can cause elevated platelets, your healthcare team must carefully rule out other possible causes and confirm ET through a combination of tests and expert analysis.

Blood Tests

The first clue often comes from a complete blood count (CBC). If your platelet count is 450,000 per microliter or higher, it raises suspicion for ET. But a high count alone isn't enough to confirm the diagnosis.

A blood smear may be done next to examine the shape and size of your blood cells under a microscope. This can show whether platelets are abnormal in appearance, which supports the diagnosis.

Genetic Testing

This test is used to identify the presence of gene mutations associated with ET, such as JAK2 V617F (found in about 50–70% of patients), CALR (in about 20–25%), or MPL (less common, around 5%). Finding one of these mutations strengthens the case for ET, but not having one doesn’t rule it out. About 10–15% of people with ET are “triple-negative,” meaning they have none of these mutations.

Bone Marrow Tests

To confirm the diagnosis, a bone marrow aspiration and biopsy is often required. This involves taking a small sample of bone marrow, usually from the hipbone, and examining it under a microscope.

In ET, the bone marrow typically shows:

• An increased number of megakaryocytes (the cells that produce platelets)
• Megakaryocytes that are large, mature-looking, and grouped in loose clusters
• No significant scarring or fibrosis (which would point to other conditions like myelofibrosis)

This test is essential not only to confirm ET but also to rule out related conditions such as prefibrotic myelofibrosis, polycythemia vera, chronic myeloid leukemia, and myelodysplastic syndromes

Imaging Tests

An ultrasound may be used to detect splenomegaly (an enlarged spleen), which is common in ET but not always present. Imaging helps assess the overall impact of the disease and can guide treatment decisions.

A Diagnosis of Exclusion and Confirmation

Diagnosing Essential Thrombocythemia requires a full evaluation, including medical history, physical exam, and a coordinated series of blood, genetic, and bone marrow tests. Doctors must exclude other conditions that mimic ET and confirm its specific features. That’s why it’s critical to work with a hematologist who specializes in myeloproliferative neoplasms (MPNs).

Summary 

Diagnosing ET involves a comprehensive evaluation that includes a medical history, physical examination, and a series of tests. Blood tests are used to check the number and appearance of blood cells and identify specific gene mutations. Bone marrow tests are used to examine the cells in the bone marrow. Imaging tests can be used to check for an enlarged spleen. The results of these tests help to confirm a diagnosis of ET and rule out other conditions. If you don't currently have an ET specialist on your team, it is important that you consult with one. Use HealthTree's ET Specialist Directory to locate a specialist near you. 

Understanding your diagnosis is just the beginning. In our ET 101 series, you can keep reading How Is Essential Thrombocythemia Staged And Classified?

Sources: 

• Essential thrombocythemia: Biology, clinical features, thrombotic risk, therapeutic options and outcome
• Essential thrombocythemia: 2024 update on diagnosis, risk stratification, and management
• Essential Thrombocytosis