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Reactive Thrombocytosis — RACP Adult Medicine MCQ

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EasyHaematologyReactive ThrombocytosisRACP Adult Medicine

A 45-year-old man presents 2 weeks after pneumonia with platelets 650 × 10⁹/L. CRP is 45 mg/L (resolving). JAK2 is negative. CALR and MPL mutations are negative. Iron studies are normal. His platelet count was 180 × 10⁹/L before the pneumonia. What is the most likely diagnosis?

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Correct answer: E — Reactive thrombocytosis (infection)

Transient thrombocytosis after infection/inflammation with elevated CRP, negative myeloproliferative neoplasm markers (JAK2, CALR, MPL), previously normal platelets, and no erythromelalgia is reactive (secondary) thrombocytosis. This is much more common than primary thrombocytosis. Reactive thrombocytosis does NOT increase thrombotic risk and does NOT require aspirin or cytoreduction. Treat the underlying cause; platelets normalise with resolution.

Reference: BSH – 2024 – Thrombocytosis Investigation