Key Takeaways

Thrombocytosis is a platelet count > 450 x 109/L. Extreme thrombocytosis describes a platelet count > 1000 x 109/L.

Thrombocytosis may be primary or secondary.

Primary thrombocytosis may be familial or acquired. The most common acquired form of primary thrombocytosis is essential thrombocythemia.

Secondary thrombocytosis, also called reactive thrombocytosis, is far more common that primary thrombocytosis, constituting about 85% of cases.

Secondary thrombocytosis is caused by myriad conditions including infections, inflammation, iron deficiency, trauma, drugs and post-splenectomy state.

Primary thrombocytosis, but not secondary thrombocytosis, is associated with an increased risk of thrombosis and hemorrhage.

Treatment of primary of thrombocytosis includes antiplatelet agents and cytoreductive therapy.

Treatment of secondary thrombocytosis is to address the underlying cause.