Reactive thrombocytosis is an elevated platelet count (> 450,000/mcL [> 450 × 109/L]) that develops secondary to another disorder.
(See also Overview of Myeloproliferative Neoplasms.)
Some causes of reactive thrombocytosis include:
Chronic inflammatory disorders (eg, rheumatoid arthritis, inflammatory bowel disease, tuberculosis, sarcoidosis, granulomatosis with polyangiitis)
Acute infection
Hemorrhage
Hemolysis
Cancer
Splenectomy or hyposplenism
There are also congenital familial thrombocytoses such as those due to thrombopoietin or thrombopoietin receptor gene mutations. For thrombocytosis that is not secondary to another disorder, see Essential Thrombocythemia.
Platelet function is usually normal. Unlike essential thrombocythemia, reactive thrombocytosis does not increase the risk of thrombotic or hemorrhagic complications unless patients have arterial disease.
With secondary thrombocytosis, the platelet count is usually < 1,000,000 platelets/mcL (< 1000 × 109/L), and the cause may be obvious from the history and physical examination and with confirmatory testing as indicated. Complete blood count and peripheral blood smear findings may help diagnose iron deficiency or hemolysis.
If a cause of secondary thrombocythemia is not obvious, patients should be evaluated for a myeloproliferative neoplasm. Such evaluation should include testing for myeloproliferative neoplasm driver mutations, cytogenetic studies (including Philadelphia chromosome or BCR-ABL assay), and possibly a bone marrow examination.
Treatment of the underlying disorder usually restores the platelet count to normal.
