Diagnostic Considerations

Elevation in the platelet count can result from physiologic or pathologic mechanisms. Essential thrombocytosis must be differentiated from secondary thrombocytosis, which may be due to an inflammatory state, iron deficiency, or recent surgery or to an underlying solid tumor or hematologic neoplasm.^[22]

British guidelines propose the following five criteria for diagnosis of essential thrombocytosis^[23]:

Sustained platelet count ≥450 × 10⁹/L
Presence of an acquired pathogenetic mutation (eg, in the JAK2, CALR or MPL genes)
No other myeloid malignancy, especially polycythemia vera, primary myelofibrosis, chronic myeloid leukemia, or myelodysplastic syndrome
No reactive cause for thrombocytosis and normal iron stores
Bone marrow aspirate and trephine biopsy showing increased megakaryocyte numbers displaying a spectrum of morphology with predominant large megakaryocytes with hyperlobated nuclei and abundant cytoplasm; reticulin is generally not increased (grades 0–2/4 or grade 0/3)

Diagnosis requires the presence of criteria 1–3 or criterion 1 plus criteria 3–5.^[23]

Differential Diagnoses

Workup

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Media Gallery

Peripheral blood smear in essential thrombocytosis showing increased platelet numbers. Courtesy Wei Wang, MD, and John Lazarchick, MD; Department of Pathology, Medical University of South Carolina.
Bone marrow biopsy in essential thrombocytosis showing increased megakaryocytes. Courtesy Wei Wang, MD, and John Lazarchick, MD; Department of Pathology, Medical University of South Carolina.