Elevated Platelet Count

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

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