Merck Manual

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Secondary Thrombocythemia

(Reactive Thrombocytosis )

By

Jane Liesveld

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

Last full review/revision Sep 2020| Content last modified Sep 2020
Click here for the Professional Version

Secondary thrombocythemia is excess platelets in the bloodstream that develops as a result of another disorder and rarely leads to excessive blood clotting or bleeding.

Platelets (thrombocytes) are cell-like particles in the blood that help the body form blood clots. Platelets are normally produced in the bone marrow by cells called megakaryocytes. In thrombocythemia, the body produces too many platelets. Thrombocythemia can be

  • Primary (essential): Caused by a disorder of platelet-forming cells (see essential thrombocythemia)

  • Secondary: Caused by a disorder that triggers increased production by normal platelet-forming cells

When thrombocythemia is caused by such an underlying disorder, the thrombocythemia is called secondary thrombocythemia (or reactive thrombocytosis) and is not classified as a myeloproliferative neoplasm.

Causes of secondary thrombocythemia include

People with secondary thrombocythemia usually have no symptoms related to the high number of platelets (unlike people with primary thrombocythemia. Symptoms of the underlying condition usually dominate.

Although an increased number of platelets might be thought to cause excessive blood clotting, this rarely happens in secondary thrombocythemia unless people also have severe arterial disease or prolonged immobility. Although some people with essential thrombocythemia have an increased risk of bleeding, this is not a concern with secondary thrombocythemia.

Secondary thrombocythemia is diagnosed—and distinguished from primary thrombocythemia—when people with high platelet counts have a condition that readily accounts for the high number of platelets.

To identify possible causes, doctors do blood tests, sometimes including genetic testing, and occasionally a bone marrow biopsy. Other tests such as radiologic tests may be needed to ascertain the cause of the platelet elevation.

Treatment is aimed at the cause of the platelet elevation. If the treatment is successful, the platelet count will return to normal.

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