Essential thrombocytosis

Essential thrombocytosis (ET) is also called essential thrombocythemia. It is a myeloproliferative neoplasm that develops when the bone marrow doesn’t work normally so it makes too many platelets. Essential thrombocytosis is a chronic disorder, which means that it develops slowly over time. It increases the risk of blood clots and bleeding.

Doctors don’t know what causes essential thrombocytosis, but some people with essential thrombocytosis have a change, or mutation, in the JAK2 (Janus kinase 2) gene. What causes this gene mutation is not known.

Essential thrombocytosis usually develops around 60 years of age. It can also develop in younger people, especially women of child-bearing age.

Pregnant women with untreated essential thrombocytosis have a risk for complications, including miscarriage, the fetus developing slower than normal and premature birth.

In rare cases, essential thrombocytosis develops into polycythemia vera (PV), myelofibrosis, a myelodysplastic syndrome or acute myelogenous leukemia (AML).


Essential thrombocytosis may not cause any symptoms. Symptoms, when present, are often related to clot formation or bleeding problems.

See your doctor if you have:

  • pain, redness, swelling and warmth in the feet and legs
  • headache
  • dizziness
  • weakness
  • vision changes such as blurred vision
  • easy bruising or bleeding
  • bleeding from the gastrointestinal (GI) tract, skin, eyes, gums or urinary tract
  • abdominal discomfort or feeling of fullness if the spleen or liver is enlarged
  • tingling in the hands and feet
  • sweating
  • itchiness
  • slightly higher than normal temperature (called a low-grade fever)


Diagnosing essential thrombocytosis begins with a trip to your family doctor or when a routine blood test suggests a problem with the blood. Your doctor will ask you about any symptoms you have and do a physical exam to check if your spleen or liver is enlarged. Based on this information, your doctor will order tests to check for essential thrombocytosis or other health problems.

Some of the same tests used to rule out or diagnose leukemia are used to diagnose essential thrombocytosis. These tests include:

  • complete blood count (CBC) to measure the number and quality of white blood cells, red blood cells and platelets
  • blood chemistry tests to show how well certain organs are working
  • reverse transcriptase polymerase chain reaction (RT-PCR) to see if cells in a sample of blood or bone marrow have the JAK2 mutation
  • bone marrow aspiration and biopsy to confirm whether or not you have essential thrombocytosis

Find out more about these tests and procedures.


Your healthcare team will create a treatment plan just for you. Treatments for essential thrombocytosis are based on your risk of developing complications such as bleeding and blood clots.

Low risk means that you have a low risk of developing complications. You are considered low risk if you don’t have any signs or symptoms of essential thrombocytosis other than a higher than normal platelet count. You are younger than 40 years of age and you don’t have any high-risk features. Most people who are low risk, especially those with no other cardiovascular risk factors, will not need treatment unless complications develop.

Intermediate risk means that you have a slightly higher risk of developing complications than people with low-risk features. You are considered intermediate risk if you are between 40 and 60 years of age and you have some symptoms, but you don’t have any high-risk features. People who are at intermediate risk may not need treatment unless complications develop.

High risk means that you are likely to develop complications. People with high-risk disease need treatment. You are considered high risk if you are older than 60 years of age and you have any of these high-risk features:

  • you have had blood clots or bleeding problems in the past
  • you have high blood pressure or diabetes
  • you smoke or are obese
  • you have a very high platelet count

Drug therapy

If you don’t have any symptoms, you probably don’t need treatments right away. The drugs used most often to treat essential thrombocytosis include:

  • hydroxyurea (Hydrea) – most commonly given drug
  • anagrelide (Agrylin)
  • interferon alfa (Intron A, Wellferon)
  • ruxolitinib (Jakavi)

Low-dose Aspirin is usually given unless there are contraindications (a symptom or condition that makes a treatment not recommended). Pregnant women may also be given Aspirin to lower the risk of complications from essential thrombocytosis.

For more information on certain drugs, go to sources of drug information.


Plateletpheresis is a procedure that removes platelets from the blood. It can temporarily lower the platelet count. Plateletpheresis is only used when the platelet count is extremely high and needs to be lowered quickly to treat clotting complications.

Plateletpheresis is done in the same way as donating blood. A needle is inserted into a vein to remove blood. After the blood is taken, a device skims the platelets from the blood. Then the plasma (the liquid portion of the blood) and the red blood cells are given back to the person.


Follow-up after treatment is an important part of cancer care. Follow-up for essential thrombocytosis is often shared among the cancer specialists (oncologists) or blood specialists (hematologists) and your family doctor. Your healthcare team will work with you to decide on follow-up care to meet your needs.

Don’t wait until your next scheduled appointment to report any new symptoms and symptoms that don’t go away.

Expert review and references