Case 13 – summary

This week’s case overs some of the issues regarding thrombocytosis.  Thrombocytosis means an elevated platelet count – usually over 450×10*9/L.  More often than not the patient is asymptomatic and it is found on a full blood count.

Causes are divided into primary or secondary.  Secondary causes are also called reactive and these are by far the most common.

Secondary causes:

  • Blood loss
  • Infection/inflammation
  • Malignancy
  • Thrombopoietin agonists e.g. romiplostim, eltromboplag
  • Rebound post chemo
  • Iron deficiency
  • Tissue damage e.g. post surgery
  • Hyposplenism

Primary causes:

  • Essential thrombocytosis
  • Polycythaemia vera
  • Myelofibrosis
  • Chronic myeloid leukaemia
  • Chronic myelomonocytic leukaemia
  • Atypical chronic myeloid leukaemia
  • Myelodysplasia (especially with the 5q deletion)
  • Myelodysplasic syndrome/myeloproliferative neoplasm unclassifiable
  • Refractory anaemia with ringed sideroblasts with thrombocytosis

History and examination

The history and examination is usually the best way to differentiate between reactive and primary causes.  Reactive thrombocytosis is clasically found post surgery in the context of sepsis and blood loss.  Otherwise in primary care without any bleeding/infection the cause is often iron deficiency and a ferritin should be checked.  History and examination should reveal any source of blood loss or infection.  A ‘screen’ for malignancy should also take place.  In hospital practice an acute rise in platelets usually indicates a reactive cause and should be monitored to ensure the count is falling once the acute phase is over.  If a high platelet count is not resolving once reactive causes have been ruled out or if there are other worrying features then further investigations are warranted.  Worrying features for a primary haematological problem include other abnormalities in the full blood count such as cytopenias, basophilia/monocytosis/eosinophilia or raised haematocrit, splenomegaly, weight loss, odd rashes or heat intolerance.


  • Full blood count with full white cell differential
  • Blood film – in reactive causes the platelets are usually small and other pointers towards infection such as toxic granulation in neutrophils
  • Ferritin
  • Infection screen (depending on history – MSU, CXR, CRP, LFTs etc.)
  • Malignancy screen (depending on history – Ca, CXR etc)
  • Bleeding history

If a primary haematological cause of thrombocytosis is suspected then further investigations depend on the blood count.  If no other abnormalities are seen then further investigations, with a JAK2-V617 mutation followed by MPL if this is negative, are appropriate.  If typical features then some clinicians may omit a bone marrow aspirate and trephine biopsy.  If concerns about CML then the BCR:ABL fusion protein is needed.  If other atypical features are present an examination of the marrow is needed to look for rarer causes of thrombocytosis (see above).

Reactive thrombocytosis

Once this is diagnosed usually it will resolve once the provoking factors have been treated. “There is no concordance with regard to management and consideration should be given to the use of aspirin 75 mg although there is no published data to support this practice.” – BCSH.  See further references below about this controversy.  Aspirin may cause side effects such as bleeding and poor wound healing.  If the platelet count is transient then side effects will usually out way potential benefits.

Essential thrombocytosis

This is a clonal myeloid blood disorder characterised by persistent thrombocytosis.  This is technically a malignancy, however does not act as such.  A clonal genetic abnormality can be demonstrated in approximately 60% of cases of ET. The JAK2 V617F mutation is detectable in 50% and the MPL mutation in up to 10%.  Patients are usually asymptommatic and the finding is usually found on routine bloods.  some patients may present with bleeding problems or thrombotic complications such as stroke or ischaemic heart disease. Patients usually have a near normal life expectancy but there is a risk of progression to myelofibrosis or acute myeloid leukaemia.  When AML occurs secondary to ET the prognosis is generally poor.

For treatment, patients are divided up into low, medium and high risk depending on platelet count, age and other risk factors. Patients should be offered clinical trials where available.  High risk patients are often treated with cytoreductive therapy such as hydroxycarbamide (interferon if younger due to potential risk of leukaemogeneisis) and aspirin.  Low and medium risk patients should be given aspirin.  Other cardiovascular risk factors should be investigated and managed appropriately.  Other second line therapies include anegrelide, busulfan and radioactive phosphorus.  JAK inhibitors are being used in myelofibrosis.

Thrombotic complications are common, however bleeding can occur, especially in high platelet counts.  This may be due to platelet dysfunction, antiplatelet agents or aquired von Willebrand’s disorder.


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