Thrombocytosis = Platelet count > 600 × 10⁹/L.
Often picked up incidentally.
Can be reactive (secondary) 🌡️ or primary (clonal) 🧬.
ℹ️ 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
Clinical Pearl:
Platelet count alone cannot tell reactive from clonal.
👉 Check CRP, ferritin, clinical context.
Persistent high count + normal inflammatory markers → think myeloproliferative disorder.
