Differential Diagnosis

Essential thrombocythemia with platelet count typically greater than 600,000/µL

Reactive thrombocytosis from:

  • inflammation

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  • infection

  • malignancy

  • iron deficiency anemia

  • acute blood loss

  • rebound from marrow suppression or immune thrombocytopenia

  • post-splenectomy

Dangerous Situations

Platelet counts greater than 1,000,000/µL are worrisome for acute thrombotic events.

Elevated platelet count with poorly functioning platelets does not present an increased risk for thrombosis.

Commonly Encountered Situations

Reactive thrombocytosis from a variety of causes is far more common than essential thrombocythemia (a chronic myeloproliferative disorder).

Suggested Additional Lab Testing

Test that reveals any of the causes of reactive thrombocytosis previously noted are valuable.

Tests to confirm the presence of essential thrombocythemia include:

  • bone marrow biopsy to show an increase in the number of megakaryocytes

  • normal RBC mass to exclude polycythemia vera

  • platelet aggregation study showing a selective impaired aggregation response only to epinephrine suggests essential thrombocythemia