Thrombocytosis (Guidelines)

Thrombocytosis is a common finding and is a frequent cause of referral for further investigation. There is a wide range of primary (eg, essential thrombocythaemia (ET), other myeloproliferative neoplasm MPN) and secondary causes as well as false or ‘spurious’ conditions mimicking thrombocytosis. Much less commonly there is a primary cause (eg, ET, other MPN). Establishing the cause therefore requires consideration of clinical features, haematological parameters and other test results.

The most common secondary (or reactive) causes of thrombocytosis are infection, inflammation, iron deficiency, tissue damage, haemolysis, severe exercise, malignancy, hyposplenism and other causes of an acute phase response. These are usually, but not always, characterized by an elevated C-reactive protein.

Identified on FBC, either incidentally or in the context of other clinical features.

• Check ferritin, CRP, blood film.
• Exclude other causes of inflammation, including infection, malignancy, surgery.
• History to include above, and specifically if there has been previous splenectomy.
• Further imaging may be helpful to inform the assessment.
• JAK2/CALR/MPL molecular mutation testing if no other obvious explanation. 
  If positive this is specific for primary causes of thrombocytosis (although a negative result does not exclude it), but the majority of cases are secondary.
• Further investigation: this will be directed by secondary care after referral or consultation.

If no obvious cause is identified following this assessment, please send EDTA blood sample via Blood Sciences for molecular testing as indicated above.  This should be requested on ICE by GPs with a view to informing the need for Haematology referral or otherwise.  It will need to arrive for testing in Aberdeen before Thursday (and avoiding public holidays) and as such is best sent on a Monday or Tuesday.  Results will be available on NHS Highland SCI store after 21 days, currently reported promptly in the 'documents' section.  Alternatively results will be available after 21 days via NHS Grampian SCI store.

• JAK2/CALR/MPL/BCR::ABL mutation positive cases.
• Mutation negative cases in the absence of another precipitant.

• As per primary care guidance.
• Note that molecular testing may be best deferred to community testing in order to exclude reactive thrombocytosis in the context of illness.

Associated thrombosis or bleeding.