Makindo Medical Notes

Thrombocytosis = Platelet count > 600 × 10⁹/L. Often picked up incidentally. Can be reactive (secondary) 🌡️ or primary (clonal) 🧬.

About

• Common haematology finding – requires detective work for the cause.
• Secondary causes are far more common than primary clonal disorders.

Causes

• Reactive (Secondary):
  • 🦠 Infection, bleeding, trauma, surgery (< usually < 1000 × 10⁹/L)
  • 🎗️ Malignancy (esp. GI, lung, ovarian) → consider weight loss, lymphadenopathy, hepatosplenomegaly
  • 🔥 Chronic inflammation (RA, IBD, vasculitis; raised CRP/ESR)
  • ⛓️ Iron deficiency anaemia
  • 🪓 Postsplenectomy or functional hyposplenism
  • 💊 Drugs (steroids, adrenaline, LMWH), pregnancy, allergy, strenuous exercise
• Primary (Clonal, Myeloproliferative):
  • Essential thrombocythaemia (ET) – platelets > 600 × 10⁹/L, normal CRP/ferritin ⚠️ Start low-dose aspirin unless > 1500 × 10⁹/L (bleeding risk). Refer haematology.
  • Polycythaemia vera (PV)
  • Chronic myeloid leukaemia (CML)
  • Myelofibrosis
  • Myelodysplastic syndromes

Clinical Assessment

• Look for infection, inflammation, anaemia, malignancy clues.
• Examine for splenomegaly, hepatomegaly, surgical scar (splenectomy).
• Livedo reticularis → vasculitis (SLE, Sneddon’s syndrome).
• Symptoms of thrombosis or bleeding in clonal disease (ET, PV).

Investigations

• 🧪 FBC: Platelet count, Hb, WCC (cytoses/cytopenias).
• 🧪 Ferritin, CRP, ESR, LFTs: Differentiate reactive vs clonal.
• 🖥️ Abdominal USS: Splenomegaly, intra-abdominal masses.
• 🫁 CXR / pelvic USS: Exclude occult neoplasia.
• 💩 FIT test: Screen for GI malignancy.
• 🧬 JAK2 mutation: Supports ET or PV diagnosis.

Management

• Reactive: Treat underlying cause (infection, iron deficiency, malignancy).
• Essential thrombocythaemia (ET):
  • Aspirin 75–300 mg/day (unless platelets > 1500 × 10⁹/L).
  • Cytoreduction (hydroxycarbamide, anagrelide, busulfan) if high-risk.
  • Plateletpheresis → rare, for end-organ ischaemia or urgent reduction.
• 📌 Always refer persistent or unexplained thrombocytosis to haematology.

References

• North Devon NHS – Thrombocytosis

Clinical Pearl: Platelet count alone cannot tell reactive from clonal. 👉 Check CRP, ferritin, clinical context. Persistent high count + normal inflammatory markers → think myeloproliferative disorder.