Haematology

Thrombocytosis (platelet count >450×10^9/L) in children is most often secondary (reactive). Primary (essential) thrombocytosis – due to a myeloproliferative neoplasm (MPN) such as essential thrombocythemia (ET) – is rare in pediatrics. By contrast, secondary thrombocytosis arises from an underlying condition and is usually transient. In children, the common triggers are reactive processes: