Thrombocytosis

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Thrombocytosis is a condition characterised by an elevated platelet count (>450 x 10⁹/L) in the blood, which may be primary (essential thrombocythaemia) or secondary (reactive thrombocytosis).

Aetiology

  • Primary thrombocytosis: essential thrombocythaemia (ET), myeloproliferative disorders (polycythaemia vera, chronic myeloid leukaemia, myelofibrosis).
  • Secondary (reactive) thrombocytosis: inflammation (infection, inflammatory bowel disease, rheumatoid arthritis), iron deficiency, malignancy, splenectomy.

Pathophysiology

  • In essential thrombocythaemia, clonal expansion of megakaryocytes leads to excessive platelet production.
  • In reactive thrombocytosis, increased platelet production occurs as a response to cytokine stimulation.
  • Increased platelet count may lead to thrombosis or, paradoxically, bleeding due to dysfunctional platelets.

Risk Factors

  • JAK2, CALR, or MPL mutations (for essential thrombocythaemia).
  • Chronic inflammatory disorders.
  • Recent surgery or trauma.
  • Iron deficiency anaemia.
  • History of splenectomy.

Signs and Symptoms

  • Asymptomatic in many cases.
  • Thrombotic events: deep vein thrombosis (DVT), pulmonary embolism (PE), stroke, myocardial infarction.
  • Microvascular symptoms: headache, dizziness, erythromelalgia (burning pain in extremities).
  • Bleeding tendency (paradoxical, due to platelet dysfunction).
  • Splenomegaly in myeloproliferative disorders.

Investigations

  • Full blood count (FBC): elevated platelet count; repeat in 4–6 weeks to confirm persistence.
  • Peripheral blood smear: done by biomed to assesses platelet morphology and identifies abnormal features.
  • JAK2, CALR, MPL mutation analysis: requested by specialist to confirm myeloproliferative neoplasms (performed in secondary care).
  • Inflammatory markers (CRP, ESR): elevated in reactive thrombocytosis due to infection or inflammation.
  • Ferritin and iron studies: to exclude iron deficiency anaemia, a common cause of reactive thrombocytosis.
  • Coeliac serology: if iron deficiency is present without an obvious cause.
  • Liver function tests (LFTs) and renal function tests: to assess for underlying systemic conditions.
  • Bone marrow biopsy: performed if primary thrombocytosis is suspected, typically in haematology.

Management

1. Confirm and Monitor

  • Repeat FBC in 4–6 weeks if thrombocytosis is incidental.
  • If platelets remain <600 x10⁹/L with no symptoms, monitor every 3–6 months.

2. Treat Underlying Causes (Reactive Thrombocytosis)

  • Manage infections, inflammatory conditions, or iron deficiency.
  • Correct iron deficiency anaemia if present.
  • Treat underlying malignancy if identified.

3. Essential Thrombocythaemia (management is done by specialist - information only)

  • Low dose aspirin: for cardiovascular risk reduction if no contraindications.
  • Cytoreductive therapy: (e.g., hydroxycarbamide, anagrelide) for high risk patients.
  • Ruxolitinib: in JAK2-positive cases refractory to hydroxycarbamide.

4. Referral

  • Urgent haematology referral: if platelets >1000 x10⁹/L or suspected myeloproliferative disorder.
  • Routine haematology referral: if thrombocytosis persists without a clear cause or iron deficiency is unexplained.
  • Cardiology referral: if thrombotic complications occur.

5. Patient Advice

  • Report symptoms like headaches, visual changes, unexplained bruising, or TIA/stroke signs.
  • Avoid NSAIDs and aspirin unless prescribed.
  • Maintain hydration to reduce clotting risk.
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