Thrombocytosis

Borders Ref Help Toolkit
NHS Borders

Definition

Persistent significant increase in platelet count >450×109/L. Reactive causes are much more common than myeloproliferative neoplasms (MPNs).

Primary causes may be suspected if there is an associated erythrocytosis or leucocytosis. Complications of MPNs include arterial or venous occlusive events.

Causes of a reactive thrombocytosis include: infection; inflammation; iron deficiency and/or bleeding; recent surgery; hyposplenism; solid organ malignancy.

If malignancy is suspected, please follow the recommendations of the Scottish Referral Guidelines for Suspected Cancer. The referral section (2.2.7) highlights that:

“Recent evidence has identified thrombocytosis as a strong risk marker for malignancy, in particular lung, endometrial, gastric, oesophageal and colorectal cancer (acronym “LEGO-C”).  With a cancer incidence of 11.6% and 6.2% in males and females respectively, these figures well exceed the 3% threshold to warrant investigation”.

Who to refer, who not to refer, how to refer

Who to refer:

  • Any patient with a persistent unexplained thrombocytosis of >450 x 109/L for at least 3 months.  OR
  • Patients with an acute arterial or venous occlusive event and a platelet count >450×109/L
  • Consider LEGO-C cancers and if suspicious features, please refer to the relevant specialty.

Who not to refer:

Patients without persistent thrombocytosis or those with evidence of an underlying cause for a reactive thrombocytosis.

How to refer:

SCI Gateway to Department of Haematology BGH

Primary care management

Primary care investigations

  • Patient history and examination. This will often diagnose or exclude the possibility of a reactive thrombocytosis.
  • Serial FBCs; blood film; CRP and ESR; ferritin, U&E’s, LFT’s, LDH.
  • The differential diagnosis of thrombocytosis is wide and most commonly secondary to non- haematological causes. Look for and treat reactive causes prior to referral.
  • CONSIDER AN URGENT CXR when another cancer is not suggested by symptoms and signs: https://www.cancerreferral.scot.nhs.uk/lung-cancer/?alttemplate=guideline

If malignancy is suspected please follow the recommendations of the Scottish Referral Guidelines for Suspected Cancer, and note the LEGO-C cancers: lung, endometrial, gastric, oesophageal and colorectal cancer

Resources and links

  • Scottish Referral Guidelines for Suspected Cancer, The Scottish Government, Jan 2019: https://www.cancerreferral.scot.nhs.uk/
  • Bailey SER et al. Clinical relevance of thrombocytosis in primary care: a prospective cohort study of cancer incidence using English electronic medical records and cancer registry data. Br J Gen Pract 2017; 67 (659): e405-e413

Editorial Information

Last reviewed: 17/07/2025

Next review date: 17/07/2027

Author(s): Charlotte Robertson.

Author email(s): HaematologyConsultants@borders.scot.nhs.uk.