Essential thrombocytosis medical therapy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Soujanya Thummathati, MBBS [2]


The majority of cases of essential thrombocytosis only require supportive care. Anti-thrombotic therapy is individualized based on patients' risk of developing thrombosis, which include aspirin therapy for low-risk patients and platelet lowering drugs (hydroxyurea, interferon-α and anagrelide) for high-risk patients.

Risk Stratification

  • Individuals with essential thrombocytosis are grouped into high-risk and low-risk groups, based on the presence or absence of risk factors for the development of complications.[1]
  • Risk factors guide therapeutic decisions.
  • The risk factors for complications include:[1]
High risk Intermediate risk Low risk
  • Age > 60 years
  • History of thrombotic events
  • Platelet count >1500 × 109/L
Age 40-60 years
Age < 40 years

Medical Therapy

  • Majority of the patients with essential thrombocytosis are asymptomatic and do not require treatment. Patients are usually diagnosed with essential thrombocytosis on routine testing for other conditions.
  • Patients at low risk for complications are placed on low dose aspirin therapy to lower the risk of thrombosis. However, there may be an increased risk of bleeding, if aspirin is initiated whilst the platelet count is very high or, if the patient is predisposed to gastrointestinal bleeds.[2] In the latter cases, aspirin is withheld.
  • In those who are at high risk for complications, platelet reduction can be achieved by hydroxyurea (hydroxycarbamide), interferon-α or anagrelide.
  • The PT1 study compared hydroxyurea in combination with aspirin to anagrelide in combination with aspirin as initial therapy for essential thrombocytosis. Hydroxyurea was superior, with lower risk of arterial thrombosis, lower risk of severe bleeding and lower risk of transformation to myelofibrosis (although the rate of venous thrombosis was higher with hydroxycarbamide than with anagrelide).[3]
  • In life threatening cases, emergent plateletpheresis may be performed where the blood of a patient is passed through an apparatus which separates out platelets and returns the remainder to the circulation.[4]

Special Care Related to Pregnancy

  • Pregnancy in patients with essential thrombocytosis is associated with a two to three fold increase in risk for spontaneous micarriage.
  • Hydroxyurea and anagrelide are contraindicated during pregnancy and nursing.[5]
  • Essential thrombocytosis can be linked with increased risk of spontaneous abortion or miscarriage in the first trimester of pregnancy. Throughout pregnancy, close monitoring of the mother for thrombosis as well as placenta is recommended to ensure blood clots are diagnosed in time for interventions.
  • Post partum, often daily injections of low dose low molecular weight heparin (e.g. enoxaparin) and low dose aspirin are prescribed as prophylaxis for several weeks as this is a period where the mother is at higher risk of developing a blood clot.[6]


  1. 1.0 1.1 Beer PA, Erber WN, Campbell PJ, Green AR (2011). "How I treat essential thrombocythemia". Blood. 117 (5): 1472–82. doi:10.1182/blood-2010-08-270033. PMC 3145107. PMID 21106990.
  2. Prognosis and treatment of essential thrombocythemia. UpToDate. Accessed on November 12, 2015.
  3. Harrison CN et al. Hydroxyurea compared with anagrelide in high-risk essential thrombocythemia. N Engl J Med. 2005;7:33-45. PMID 16000354.
  4. Plateletpheresis. Wikipedia. Accessed on November 12, 2015.
  5. Marie-Cecile Valera, Olivier Parant, Christophe Vayssiere, Jean-Francois Arnal & Bernard Payrastre (2011). "Essential thrombocythemia and pregnancy". European journal of obstetrics, gynecology, and reproductive biology. 158 (2): 141–147. doi:10.1016/j.ejogrb.2011.04.040. PMID 21640467. Unknown parameter |month= ignored (help)
  6. Essential thrombocythemia. Orphanet journal of rare diseases. Accessed on November 11, 2015.

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