Secondary Thrombocytosis

Updated: Dec 24, 2018
  • Author: Koyamangalath Krishnan, MD, FRCP, FACP; Chief Editor: Srikanth Nagalla, MBBS, MS, FACP  more...
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Platelets are acute-phase reactants; therefore, they increase in response to various stimuli, including systemic infections, inflammatory conditions, bleeding, and tumors. [1, 2, 3] This is called reactive or secondary thrombocytosis, which is a benign form of thrombocytosis. In contrast, clonal thrombocytosis (primary or essential thrombocytosis) is an unregulated abnormality of platelet production due to a clonal expansion of bone marrow progenitor cells. [4, 5]



Secondary thrombocytosis (reactive thrombocytosis) may be due to the overproduction of proinflammatory cytokines, such as interleukin (IL)-1, IL-6, and IL-11, that occurs in chronic inflammatory, infective, and malignant states. [6, 7, 8, 9] The presence of elevated IL-1, IL-6, C-reactive protein (CRP), granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor (GM-CSF) in individuals with these conditions suggests that these cytokines may be involved in secondary thrombocytosis.



Secondary thrombocytosis (reactive thrombocytosis) is a relatively common condition. The incidence varies with the underlying condition. The incidence of postsplenectomy secondary thrombocytosis is approximately 75-82%. [10]

Overall, secondary thrombocytosis occurs in 3-13% of hospitalized children. However, in a Greek study of children 10 days to 8 years old who were hospitalized with viral pneumonia, [9] and an Italian study of children 1 to 24 months old who were hospitalized for community-acquired infections, [11] approximately half had thrombocytosis.

Secondary thrombocytosis is more common than primary thrombocytosis. In a series from a large US university hospital that included 280 patients with extreme thrombocytosis (platelet count of 1,000 x 109/L or greater), 82% had secondary thrombocytosis. [12]


Race-, Sex-, and Age-related Demographics

No race predilection exists for secondary thrombocytosis (reactive thrombocytosis). No sex predilection exists for secondary thrombocytosis, except that iron deficiency is more prevalent in females during childbearing years. No age predilection exists for secondary thrombocytosis. [11, 13]