Thrombocytosis is a raised number of platelets, usually defined as ≥ 450 x 10^9 

Thrombocytosis may be divided into : 

  • Spurious 
    • Caused by non-platelet structures in the blood which are counted as platelets by modern automated counters 
    • Examples include 
      • Cryoglobulin crystals 
      • Microspherocytes (eg from severe burns) 
      • Schistocytes 
      • Pappenheimer bodies 
      • Bacteria

  • Primary thrombocytosis 
    • Increase in platelets caused by alterations targeting the haematopoietic cells 
    • Causes are
      • Essential thrombocytheameia 
        • Megakaryocyte proliferation 
        • Not meeting WHO criteria for CML, PV, PMF or MDS
        • Presence of JAK 2 or other clonal marker and no evidence of reactive thrombocytosis
        • Increases risk of both thrombosis and bleeding 
        • Treatment: 
          • High risk patients (aged >60 OR platelet count >1500 OR disease-related thrombotis/haemorrhage) 
            • Hydroxycarbamide plus aspirin 
            • ? interferon alpha in young patients
          • Other patients 
            • Aspirin only
      • Polycythaemia Vera
      • Myelofibrosis 
      • Chronic myeloid leukaemia

  • Secondary/reactive thrombocytosis 
    • Reactive to 
      • Infection 
      • Inflammation 
      • Post-operative/trauma 
      • Iron deficiency 
      • Hyposplenism
      • Haemorrhage 
      • Malignancy 
      • Drugs 
        • Corticosteroids 
        • Adrenaline 
    • Rarely causes complications 
    • Treat underlying cause 

Small print gem: extremely high platelet levels (>1500 x 10^9) result in more causes of bleeding than thrombosis 

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