Definition
Persistent significant increase in platelet count >450×109/L. Reactive causes are much more common than myeloproliferative neoplasms (MPNs).
Causes.
- Primary causes can be associated with an associated erythrocytosis or leucocytosis. Haematological conditions associated with a raised platelet count including essential thrombocythaemia, polycythaemia vera, primary myelofibrosis, chronic myeloid leukaemia, myelodysplastic syndromes, and unclassified myeloproliferative disorders. Complications of MPNs include arterial or venous occlusive events.
- Reactive thrombocytosis (commonest cause): infection; inflammation; iron deficiency and/or bleeding; recent surgery; hyposplenism; solid organ malignancy.
THROMBOCYTOSIS & CANCER – the ‘LEGO-C’ group.
Thrombocytosis is a risk marker for malignancy. This especially applies to the ‘LEGO-C’ group –Lung, Endometrial, Gastric, Oesophageal and Colorectal cancer.
The Scottish Referral Guidelines for Suspected Cancer report higher all-cancer incidence in those aged ≥40 with new thrombocytosis (platelets>400 x 109 /L). The incidence is 11.6% in men and 6.2% in women (cf controls of 4.1% / 2.2% respectively), well exceeding the threshold for referral for malignancy.
Thrombocytosis occurring with an elevated alkaline phosphatase (ALP), has a yet-higher PPV for cancer.
Please see Primary Care Management for more detail including initial investigation.
IK, KD & CM 2/12/25
Who to refer:
- Consider LEGO-C cancers and if suspicious features, please refer to the relevant specialty.
- 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.
Who not to refer:
Patients without persistent thrombocytosis or those with evidence of an underlying cause for a reactive thrombocytosis; and where relevant an associated cancer diagnosis has been considered / excluded.
How to refer:
SCI Gateway to Department of Haematology WGH or St John’s Hospital.
For all those with an unexplained thrombocytosis, consider whether there might be associated malignancy:
- Patient history and examination, in particular considering the LEGO-C cancers: lung, endometrial, gastric, oesophageal and colorectal.
- where there are no tumour-specific symptoms arrange a USC chest X-ray.
- when combined with non-specific symptoms such as significant weight loss or GP ‘gut feeling’, consider referral for further cancer investigation eg GP direct access to imaging pathway / see the Scottish Referral Guidelines for Suspected Cancer
- This process will often diagnose or exclude the possibility of a reactive thrombocytosis.
Please also consider
- The differential diagnosis of thrombocytosis is wide and most commonly secondary to non-haematological causes. Look for and treat reactive causes prior to referral
- Serial FBCs; blood film; CRP and ESR; ferritin, C&Es, LFTs, LDH
- Significant reactive thrombocytosis can take 4-8 weeks to return to baseline
- Thrombocytosis associated with chronic inflammatory conditions may not resolve.
