Megakaryocytic proliferation and atypia, without reticulin fibrosis >grade 1, accompanied by increased age-adjusted bone marrow cellularity, granulocytic proliferation, and often decreased erythropoiesis
Not meeting the WHO criteria for BCR-ABL1+ CML, PV, ET, myelodysplastic syndromes, or other myeloid neoplasms
Presence of JAK2, CALR, or MPL mutation or in the absence of these mutations, presence of another clonal marker,* or absence of minor reactive bone marrow reticulin fibrosis¶
Minor criteria
Presence of at least 1 of the following, confirmed in 2 consecutive determinations:
Anemia not attributed to a comorbid condition
Leukocytosis ≥11 × 109/L
Palpable splenomegaly
LDH increased to above upper normal limit of institutional reference range
Diagnosis of prePMF requires meeting all 3 major criteria, and at least 1 minor criterion
CML: chronic myeloid leukemia; ET: essential thrombocythemia; PMF: primary myelofibrosis; PV: polycythemia vera; WHO: World Health Organization * In the absence of any of the 3 major clonal mutations, the search for the most frequent accompanying mutations (eg, ASXL1, EZH2, TET2, IDH1/IDH2, SRSF2, SF3B1) are of help in determining the clonal nature of the disease. ¶ Minor (grade 1) reticulin fibrosis secondary to infection, autoimmune disorder or other chronic inflammatory conditions, hairy cell leukemia or other lymphoid neoplasm, metastatic malignancy, or toxic (chronic) myelopathies.