Reactive Thrombocytosis (Secondary Thrombocythemia)

Reactive thrombocytosis is an elevated platelet count ( 450,000/mcL [ 450 10/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

• Iron deficiency

• Hemolysis

• Cancer

• Splenectomy or hyposplenism

There are also congenital familial thrombocytoses such as those due to thrombopoietin and thrombopoietin receptor gene mutations. For thrombocytosis that is not secondary to another disorder, see Essential Thrombocythemia.

Platelet function is usually normal. Unlike in 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/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 suggest iron deficiency or hemolysis.

If a cause of secondary thrombocythemia is not obvious, patients should be evaluated for a myeloproliferative neoplasm. Such evaluation may include testing for myeloproliferative neoplasm driver mutations, cytogenetic studies, including Philadelphia chromosome or BCR-ABL assay, and possibly bone marrow examination, especially in patients with anemia, leukopenia, and/or hepatosplenomegaly.

Treatment of the underlying disorder usually returns the platelet count to normal.