Diagnostic Criteria for Essential Thrombocytosis (ET)

Essential Thrombocytosis (ET) is the only chronic myeloproliferative disorder (MPD) without a specific phenotype. Because isolated thrombocytosis can be the initial clinical manifestation of polycythemia vera (PV), primary myelofibrosis (PMF), or chronic myelogenous leukemia, ET is not only a diagnosis of exclusion, it should also not be considered a single disease entity.

Diagnostic criteria for essential thrombocytosis (ET)

  • Persistent thrombocytosis more than 400000/µL in the absence of a reactive cause*
  • Absence of iron deficiency (normal serum ferritin for sex)
  • JAK2 V617F assay (peripheral blood; expression establishes the presence of an MPD but not its type; absence does not exclude an MPD)
  • Hemoglobin less than 16 g/dL in a man or less than 14 g/dL in a woman (hematocrit < 47% in a man or < 44% in a woman) in the absence of splenomegaly; otherwise, red cell mass and plasma volume determinations are mandatory if a JAK2 V617F assay is positive
  • Negative Bcr-Abl FISH (peripheral blood) if a JAK2 V617F assay is negative
  • If there is anemia, macrocytosis, or leukopenia, or evidence of extramedullary hematopoiesis (ie, circulating nucleated erythrocytes, immature myelocytes, or splenomegaly), a bone marrow examination (including flow cytometry and cytogenetics) is mandatory regardless of JAK2 V617F expression status

MPD indicates myeloproliferative disorder; and FISH, fluorescent in situ hybridization.
*As indicated in the text, MPD patients represent only a minority of thrombocytosis patients in general but constitute most of those with persistent thrombocytosis in the absence of a definable cause.



  1. Spivak JL, Silver RT. The revised World Health Organization diagnostic criteria for polycythemia vera, essential thrombocytosis, and primary myelofibrosis: an alternative proposal. Blood. 2008 Jul 15;112(2):231-9. [Medline]
  2. Vannucchi AM, Guglielmelli P, Tefferi A. Polycythemia vera and essential thrombocythemia: algorithmic approach. Curr Opin Hematol. 2018 Mar;25(2):112-119. [Medline]


Created Jan 21, 2019.