thrombocytosis

Thrombocytosis is a condition in which the number of platelets in the blood is higher than normal. It is usually defined as a platelet count above 450,000 per microliter. Thrombocytosis can be categorized as primary (or clonal) thrombocytosis, arising from an intrinsic problem in platelet production, or secondary (reactive) thrombocytosis, occurring in response to another condition.

Primary thrombocytosis most commonly reflects a myeloproliferative neoplasm, with essential thrombocythemia being the best described. In these disorders, platelets are produced in excess by the bone marrow, and patients may be at increased risk of thrombosis or, less commonly, bleeding. Common mutations associated with primary thrombocytosis include JAK2, CALR, and MPL. Diagnosis typically involves complete blood count, blood smear, exclusion of iron deficiency or inflammation, and genetic testing; bone marrow examination may be used to define the underlying disorder.

Secondary thrombocytosis, or reactive thrombocytosis, is more common and occurs in association with infections, inflammatory or autoimmune diseases, iron deficiency, acute blood loss, malignancy, surgery, or splenectomy. It is usually transient and related to the underlying condition; management focuses on treating that condition. In some cases, iron repletion or removal of the provoking factor normalizes platelet counts.

Evaluation of thrombotic risk and treatment decisions depend on whether thrombocytosis is primary or reactive. Reactive thrombocytosis often requires no specific therapy beyond addressing the underlying cause, while primary thrombocytosis may require antiplatelet therapy and, in higher-risk cases, cytoreductive treatment. Regular follow-up with healthcare providers is advised to monitor platelet counts and associated risks.