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Essential Thrombocythaemia (ET)

Updated: Jun 25, 2023

Essential Thrombocythaemia (ET)

Content guide

What is essential thrombocythaemia?

Essential thrombocythaemia (ET) is a rare blood disorder that causes your body to produce too many platelets. Platelets are blood cells that help your blood clot and stop bleeding. Too many platelets can increase your risk of blood clots in your arteries or veins, leading to severe complications such as stroke, heart attack, or pulmonary embolism.

Names for this disorder

ET is also known as essential thrombocytosis, primary thrombocythaemia, or primary thrombocytosis. These names all refer to the same condition.

How common is ET?

ET is estimated to affect about 30 people per million in the general population. It can occur at any age but is more common in older adults. The average age of diagnosis is around 60 years. ET affects slightly more women than men.


ET is diagnosed by a blood test that measures the number of platelets in your blood. However, having a high platelet count does not necessarily mean you have ET, as there are other possible causes of elevated platelets.

Reasons your platelets may be high.

Some of the common reasons why your platelets may be high include:

  • Inflammation or infection

  • Iron deficiency

  • Splenectomy (removal of the spleen)

  • Reactive thrombocytosis (a temporary increase in platelets due to another condition)

  • Certain medications

  • Pregnancy

If your platelet count is high, your doctor will perform further tests to rule out these causes and confirm the diagnosis of ET.

Signs and symptoms

Many people with ET do not have any signs or symptoms and are diagnosed incidentally during a routine blood test. However, some people may experience symptoms related to the high platelet count or the increased risk of blood clots. These symptoms may include:

  • Headaches

  • Dizziness

  • Vision problems

  • Tingling or numbness in the hands or feet

  • Redness or warmth in the face or extremities

  • Bleeding or bruising easily

  • Abdominal pain or discomfort

  • Fatigue

  • Itching

Diagnostic tests

In addition to a blood test, your doctor may perform other tests to confirm the diagnosis of ET and assess your risk of complications. These tests may include:

- Bone marrow biopsy: A small sample of bone marrow (the soft tissue inside your bones where blood cells are made) is taken and examined under a microscope. This can show if there are any abnormal changes in the cells that produce platelets.

- Genetic tests: A sample of your blood or bone marrow is analyzed for specific genetic mutations associated with ET. The most common mutation is called JAK2 V617F, which affects about half of people with ET. Other mutations include CALR, MPL, and TET2.

- Ultrasound: An imaging test that uses sound waves to create pictures of your internal organs. This can show if you have an enlarged spleen or liver, which can occur in some people with ET.


If you have ET, your doctor may prescribe medications to reduce your risk of clotting. These may include aspirin, which prevents platelets from sticking together, or anticoagulants, which slow down the clotting process. You may also need regular blood tests to monitor your platelet level and adjust your medication dose.

Some people with ET may also need therapies to reduce their platelet count. These may include hydroxyurea, which slows down the production of platelets in the bone marrow, or anagrelide, which blocks the maturation of platelets. Sometimes, you may need a plateletpheresis procedure, which involves removing excess platelets from your blood through a machine.

The prognosis for people with ET varies depending on their age, medical history, and response to treatment. Most people with ET have an average life expectancy and can manage their condition with medication and regular check-ups. However, some people may develop complications affecting their quality of life or require more intensive treatment. In rare cases, ET can progress to a more severe form of blood cancer called acute myeloid leukemia (AML).


ET is a chronic condition requiring regular monitoring and follow-up with a hematologist-oncologist, a doctor specializing in blood diseases and cancers. People with ET should also care for their general health by avoiding smoking, staying hydrated, exercising regularly, and eating a balanced diet. They should also report any symptoms or changes in their health to their doctor as soon as possible.

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