Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Thrombosis or major platelet-type bleeding
Stroke, acute coronary syndrome, limb or splanchnic ischaemia, intracranial haemorrhage, uncontrolled mucosal bleeding or procedural haemorrhage requires immediate vascular care and parallel assessment of platelet number and function.
Action: Use the relevant emergency pathway, send FBC with film, coagulation, renal and liver tests and group samples, stop contributory antiplatelet medicines when appropriate, involve haematology urgently, test for acquired von Willebrand syndrome with extreme counts, and do not delay definitive haemostasis or treatment of the underlying disorder.
Synopsis
Distinguish reactive from clonal thrombocytosis, recognise paradoxical bleeding and acquired platelet dysfunction, and direct urgent or definitive treatment at the mechanism rather than the platelet count alone.
Confirm genuine thrombocytosis with a repeat FBC and film; the platelet count alone does not distinguish a reactive process from a myeloproliferative neoplasm.
First-line cause assessment includes history, examination, serial counts, ferritin and iron studies, CRP or ESR, renal and liver function and review for infection, inflammation, bleeding, surgery, splenectomy and malignancy.
Persistent unexplained thrombocytosis requires haematology assessment with JAK2 V617F, then CALR and MPL or an appropriate myeloid panel; BCR::ABL1 testing and marrow examination depend on phenotype.
Key red flags
New focal neurology, chest pain, painful pale limb, abdominal pain or unusual-site thrombosis may be a clonal myeloproliferative presentation even when thrombocytosis was previously labelled reactive.
Count-related paradox
Mucosal bleeding at an extreme count is not reassurance against clotting; it requires acquired VWF assessment before aspirin.
Investigation priorities
01
First-line: repeat FBC and blood filmFirst stepFirst line
Verify persistence and identify spurious counts or another myeloid phenotype.
02
First-line: reactive-cause screenFirst line
Find common reversible drivers before labelling a clonal disorder.
Management branches
New thrombocytosisConfirm and seek a driver
An automated platelet count is at least 450 × 10⁹/L or unexpectedly rising.
Repeat the FBC and inspect a film, comparing prior counts and the timing of acute illness or surgery.
Assess iron status, inflammation, infection, bleeding, malignancy, splenectomy and renal or liver disease from history, examination and targeted tests.
Key medicines
Desmopressin for selected uraemic bleedingGive 0.3 micrograms/kg intravenously diluted and infused over 20–30 minutes shortly before the haemostatic challenge; use as a single monitored dose unless a haemostasis specialist explicitly directs repetition.
Tranexamic acidFor suitable adult mucosal bleeding, a common regimen is 1 g orally three times daily for the shortest required course; use the exact local or product protocol and reduce the dose in renal impairment.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.