What is essential thrombocythaemia (ET)?

Essential thrombocythaemia (ET) is a slow-growing blood cancer. It is where the bone marrow makes too many blood clotting cells, called platelets. This means there are more platelets than normal in the blood.

ET usually develops very slowly. In most people, it does not shorten their lives. ET is more common in people aged over 50, but it can affect people at any age.

To understand ET and its treatment, it can help to know more about your blood and bone marrow.

Symptoms of essential thrombocythaemia (ET)

Having too many platelets in the blood does not always cause symptoms. Some people are diagnosed with ET after they have a blood test for another reason.

Possible symptoms of ET include:

  • headaches
  • dizziness
  • redness, swelling or pain in the hands or feet
  • tiredness
  • difficulty in concentrating
  • itchy skin
  • bone pain.

Sometimes symptoms develop because of complications of ET. For example, this could be a blood clot caused by too many platelets in the blood. Less commonly, you may have unusual bleeding or bruising if the platelets in your blood are not working properly.

Possible complications of ET

  • Gout

    People with ET can develop red, painful and swollen joints. This is caused by a condition called gout. Gout can happen when the body breaks down more blood cells than normal.

    When the body breaks down cells it makes uric acid. Normally the kidneys remove this acid from the blood and pass it out of the body in urine (pee). If the body breaks down more cells than the kidneys can get rid of, uric acid builds up in the blood. Crystals that form from uric acid get into the joints and cause the symptoms of gout.

    Gout usually affects the big toe, but other joints can be affected. Your doctor will check the level of uric acid in your blood. If it is higher than normal, they may give you tablets called allopurinol. Allopurinol prevents gout by helping your kidneys to get rid of uric acid.

  • Enlarged spleen

    The spleen sits on the left side of the tummy (abdomen), just under the ribs. It is usually about the size of a fist.

    The spleen:

    • helps fight infection 
    • stores and breaks down blood cells.

    ET can cause your spleen to grow bigger than normal. Sometimes this causes symptoms. These include discomfort on the left side of the tummy and feeling full quickly when eating

  • Blood clots

    Some people with ET have a higher risk of developing blood clots.

    If you have any symptoms you think may be caused by a blood clot, contact a doctor urgently. If you cannot speak to a doctor, call 999 for an ambulance or go to A&E.

  • Bleeding or bruising

    Sometimes ET can cause abnormal bleeding, but this is less common than a blood clot. Bleeding is most likely to happen if your platelet levels are very high (more than 1500 x 109per litre). It may be heavier than normal and take longer to stop.

    Symptoms may include:

    • nosebleeds
    • bruising easily
    • abnormal vaginal bleeding
    • bleeding gums
    • very dark stools (poo) or dark vomit, caused by bleeding in the stomach or bowel.

    Tell your doctor if you notice any signs of abnormal bleeding.

    If you think you are bleeding from the stomach or bowel, or if bleeding is heavy or will not stop, contact a doctor urgently. If you cannot speak to a doctor, call 999 for an ambulance or go to A&E.

  • Myelofibrosis

    A very small number of people with ET may develop a more serious condition called myelofibrosis. Myelofibrosis causes scarring of the bone marrow.

Diagnosis of essential thrombocythaemia (ET)

You are usually diagnosed with ET by a doctor who specialises in treating blood disorders (haematologist). Your GP may have suspected ET based on the results of a blood test (called a full blood count). This test counts the number of red blood cells, white blood cells and platelets in the blood. People with ET will have a high platelet count.

Other conditions can cause an increase in platelets in the blood, for example:

  • an infection
  • inflammatory conditions such as rheumatoid arthritis
  • a lack of iron in the blood.

Your doctor will need to rule these things out before they diagnose ET.

You usually need different blood tests. Some people have tests on their bone marrow.

Blood tests to check for gene changes

Genes carry the instructions a cell needs to work properly. Certain genes control how many blood cells the bone marrow makes. Changes (mutations) in some of these genes can cause ET.

You usually have blood tests to check if you have any of these gene changes. These changes happen in the cells during your life. It is not a gene change you are born with and cannot be passed on in your family.

Changes in the following genes can cause ET:

  • JAK2 – about 55 in a 100 people (55%) with ET have a change in the JAK2 gene.
  • CALR – about 25 in a 100 people (25%) with ET have a change in the CALR gene.
  • MPL – about 3 in a 100 people (3%) with ET have a change in the MPL gene.

About 25 in 100 people (25%) with ET do not have a mutation in any of these genes. This is called triple negative ET.

Bone marrow test

Your doctor may want to take a sample of bone marrow (biopsy) to look at under a microscope. They usually remove it from the back of your hip bone (pelvis).

Waiting for test results can be a difficult time. It may help to talk to your family, friends or specialist nurse.

Treatment for essential thrombocythaemia (ET)

Treatment for ET aims to reduce complications, particularly blood clots. Your doctor will check your condition by doing regular blood tests.

The treatment you have will depend on your risk of developing complications. Your doctor will assess if you have a low, medium or high risk. They will base this on:

  • your age
  • your symptoms
  • the number of platelets in your blood
  • any gene changes (mutations) you have
  • if you have had a blood clot before
  • if you have other conditions, such as diabetes.

You may be invited to join a clinical trial looking at new ways of treating ET.

Reducing risk factors for heart disease and stroke

Because ET can cause blood clots, it is important to reduce your risk of heart disease and stroke. If you have any health conditions that could increase your risk, your doctors and nurses will make sure they are well controlled. This includes conditions such as:

  • diabetes
  • high blood pressure
  • high cholesterol.

Your doctors and nurses will give you advice about any lifestyle changes you can make to help to reduce your risk. They usually advise you to:

  • drink plenty of fluids


Most people with ET are treated with aspirin. Aspirin affects the way platelets stick together and helps prevent clots. It does not affect the numbers of platelets in the blood.

One of the side effects of aspirin is an increased risk of bleeding and ulcers in the stomach. If you are taking aspirin, ask your doctor for advice about painkillers. Certain types of painkillers, such as ibuprofen, may not be suitable for you while you are taking aspirin.

Treatment to reduce platelet numbers

If you have a high risk of blood clots, you will usually have treatment to reduce the numbers of platelets in your blood. This is called cytoreductive therapy. Different types of drugs can be used. Your haematologist or specialist nurse will talk to you about your treatment.


You may have chemotherapy to reduce the number of platelets in the blood.

Hydroxycarbamide (HC) is the most commonly used chemotherapy drug to treat ET. You take it as a capsule or tablet. It can cause side effects, but these are usually mild.

Taking HC for a long time can increase your risk of getting a skin cancer. It is important that you protect your skin from the sun. You also need to check for any changes in your skin during and after treatment with HC. Your haematologist or specialist nurse can tell you more about this.

Another chemotherapy drug called busulfan may sometimes be used. You have it as a tablet. The side effects are like the side effects of hydroxycarbamide. If you take busulfan for a long time, it may slightly increase your risk of developing leukaemia.

Interferon alpha

Interferon is a natural substance made by the body. It can also be made as a medicine. It slows down the rate at which the bone marrow makes blood cells, including platelets.

If you are pregnant and have high-risk ET, your doctor may give you interferon. They may also prescribe it if you are planning to get pregnant or to make someone pregnant but need treatment.


Anagrelide is a drug that is usually given after you have already had other treatments to reduce your platelet levels. You take it as a capsule.

Side effects can include headaches and changes to your heart rate and rhythm. Some research suggests that anagrelide may increase the risk of getting myelofibrosis.

Anagrelide does not seem to affect your fertility. But you should not take it if you are pregnant or trying to get pregnant. It is important to use effective contraception when taking anagrelide.

Radioactive phosphorus (32P)

Rarely, a treatment called radioactive phosphorus may be used. A doctor gives it to you as an injection into the vein. It gives a dose of radiation to the bone marrow and reduces the number of platelets being made. You usually only have this treatment when other treatments are not suitable or have not worked.

The effects of one treatment can last from months to years. Having long-term treatment with radioactive phosphorus increases the risk of leukaemia.

Pregnancy, fertility and essential thrombocythaemia (ET)

If you are planning to get pregnant or to make someone pregnant in the next few months, talk to your doctor first.

ET can increase the risks of complications in pregnancy. But with risk-reducing treatments and careful monitoring during pregnancy, most women have healthy babies. Your haematologist and obstetrician (doctor who specialises in pregnancy) will work together to give you the best care during your pregnancy.

During pregnancy your doctor usually advises you to take aspirin daily. This reduces the risk of complications from blood clots for both you and the baby. If you need other treatment to reduce your risk of complications, your doctor may advise having interferon (IFN).

Chemotherapy and some other treatments may affect the development of an unborn baby. Doctors usually advise against getting pregnant or making someone pregnant during these treatments and for a few months after. It is important to use effective contraception.

Chemotherapy may affect fertility. If this is a concern for you, talk to your doctor before starting treatment. We have more information about fertility in men and women.

Living with essential thrombocythaemia (ET)

You will need regular check-ups and blood tests. If you are worried or notice any new symptoms between appointments, tell your haematologist or specialist nurse or as soon as possible.

Making lifestyle changes to reduce your risk of complications can sometimes be challenging. You may find it easier to make changes as part of a group or with help from others. Tell your GP, practice nurse or haematology team if you are finding it difficult. There is lots of support available to help you live a healthier lifestyle.

Your feelings

Everyone has their own way of dealing with the different feelings they experience. You may find it helpful to talk things over with family and friends, or your specialist doctor or nurse.

Macmillan is also here to support you. If you would like to talk, you can:

The organisations below also offer information and support: 

  • MPN Voice

    MPN Voice is a support network for people with MPNs (myeloproliferative neoplasms) providing information and support.

  • Leukaemia Care

    Leukaemia Care is a national blood cancer support charity for people with leukaemia and other blood disorders. It has regional support groups.

  • Blood Cancer UK 

    Blood Cancer UK is a blood cancer research charity that provides information and support on any type of blood cancer.

Reviewed: 08 November 2019
Reviewed: 08/11/2019
Next review: 08 May 2022
Next review: 08/05/2022

This content is currently being reviewed. New information will be coming soon.