Merck Manual

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Reactive Thrombocytosis (Secondary Thrombocythemia)

By

Jane Liesveld

, MD, James P. Wilmot Cancer Institute, University of Rochester Medical Center

Last full review/revision Jul 2022| Content last modified Sep 2022
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Reactive thrombocytosis is an elevated platelet count (> 450,000/mcL [> 450,000 × 109/L]) that develops secondary to another disorder.

Some causes of reactive thrombocytosis include

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 Essential Thrombocythemia Essential thrombocythemia (ET) is a myeloproliferative neoplasm characterized by an increased platelet count, megakaryocytic hyperplasia, and a hemorrhagic or microvascular vasospastic tendency... read more .

Platelet function is usually normal. Unlike in essential thrombocythemia Essential Thrombocythemia Essential thrombocythemia (ET) is a myeloproliferative neoplasm characterized by an increased platelet count, megakaryocytic hyperplasia, and a hemorrhagic or microvascular vasospastic tendency... read more , reactive thrombocytosis does not increase the risk of thrombotic or hemorrhagic complications unless patients have severe arterial disease or prolonged immobility.

With secondary thrombocytosis, the platelet count is usually < 1,000,000/mcL (< 1,000,000 × 109/L), and the cause may be obvious from the history and physical examination (perhaps with confirmatory testing). Complete blood count and peripheral blood smear findings may help suggest iron deficiency or hemolysis.

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

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