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Essential Thrombocytosis

Essential thrombocytosis (ET), or primary thrombocythemia, is a rare disorder in which the body produces too many platelets for unknown reasons. This can cause abnormal blood clotting or bleeding. The condition usually affects people in middle age, although it can be seen in younger patients, especially in women less than 40 years old. Patients with ET have an excellent chance of living a normal life span if they are properly monitored and treated as necessary. A small number of patients may develop acute leukemia or a bone marrow disorder called myelofibrosis.

Risk Factors

The causes of ET are still unknown. About half of ET patients have a mutation called JAK2V617F within their blood-forming cells, which leads to many characteristic features of the disease.

Some risk factors associated with ET include:

  • Gender -- Women are 1.5 times more likely than men to develop the condition.
  • Age -- People older than 60 are most likely to develop the condition, although 20 percent of those affected are younger than 40.
  • Environment - Exposure to chemicals or to electrical wiring may increase an individual's risk for the condition.


Many patients do not have any symptoms, and are diagnosed after blood counts as part of a routine check-up reveal a high platelet count. Symptoms, if present, include fatigue, or blood vessel disturbances or bleeding.

Blood vessel disturbances or bleeding can result in:

  • Headache
  • Vision disturbances or silent migraines
  • Dizziness or lightheadedness
  • Coldness or blueness of fingers or toes
  • Burning, redness, and pain in the hands and feet
  • Easy bruising, nosebleeds or heavy periods
  • Gastrointestinal bleeding or blood in the urine

Blood clots can be quite serious, leading to strokes or heart attacks.


ET is often detected on blood tests done for other reasons, before there are any symptoms. Additional tests may include:

  • Complete blood count - to measure the amount of platelets in the blood
  • Blood smear - examination of a blood sample under a microscope to see if platelets are enlarged or clumped together
  • Genetic testing - to look for mutations to the JAK2 gene
  • Bone marrow tests - Your doctor may take a sample of bone marrow fluid to study for abnormal cells, or of bone marrow tissue to study the number of large cells that produce platelets.


Treatments for ET can vary depending on a patient's symptoms. Some patients may not need active treatment but should still be monitored by a physician expert. Treatments include:

  • Low-dose aspirin - may be given to reduce the risk of blood clotting
  • Platelet-lowering medications - Drugs including hydroxyurea, anagrelide, and interferon may be prescribed to reduce the risk of bleeding or clotting complications.
  • Plateletpheresis - Following an emergency such as a stroke or severe clotting issue, this procedure can quickly lower your platelet count. Blood is removed through a tube, stripped of platelets, and returned through another tube.

At Johns Hopkins

The Johns Hopkins Center for Myeloproliferative Disorders coordinates the care of patients with ET and other related disorders and conducts research in these areas.


For more information, see the website for the MPN Research Foundation