Table 2 2016 World Health Organization diagnostic criteria for primary myelofibrosis

	*Primary myelofibrosis (PMF)* ^a
	Prefibrotic/early PMF (pre-PMF)	Overt PMF
Major criteria
1	Megakaryocytic proliferation and atypia^b, without reticulin fibrosis > grade 1^c, accompanied by increased age-adjusted BM cellularity, granulocytic proliferation and often decreased erythropoiesis	Megakaryocyte proliferation and atypia^b accompanied by either reticulin and/or collagen fibrosis (grade 2 or 3)
2	Not meeting WHO criteria for BCR-ABL1 + CML, PV, ET, MDS, or other myeloid neoplasm	Not meeting WHO criteria for BCR-ABL1 + CML, PV, ET, MDS or other myeloid neoplasm
3	Presence of JAK2, CALR, or MPL mutation or in the absence of these mutations, presence of another clonal marker^d or absence of minor reactive BM reticulin fibrosis^e	Presence of JAK2, CALR, or MPL mutation or in the absence, the presence of another clonal marker^d or absence of evidence for reactive BM fibrosis^f
Minor criteria
1	Presence of one or more of the following, confirmed in two consecutive determinations:	Presence of one or more of the following confirmed in two consecutive determinations:
	• Anemia not attributed to a comorbid condition	• Anemia not attributed to a comorbid condition
	• Leukocytosis ≥ 11 × 10⁹/L	• Leukocytosis ≥ 11 × 10⁹/L
	• Palpable splenomegaly	• Palpable splenomegaly
	• LDH level above the upper limit of the institutional reference range	• LDH level above the upper limit of the institutional reference range
		• Leukoerythroblastosis

Table adapted from Barbui T et al. Blood Cancer J. 2015; 5:e337¹⁰³. and Arber et al. Blood 2016;127:2391–2405²
BM, bone marrow; CML, chronic myeloid leukemia; MDS, myelodysplastic syndrome; LDH, serum lactate dehydrogenase
^aDiagnosis of prefibrotic/early PMF requires all three major criteria and at least one minor criterion. Diagnosis of overt PMF requires meeting all three major criteria and at least one minor criterion
^bSmall-to-large megakaryocytes with aberrant nuclear/cytoplasmic ratio and hyperchromatic and irregularly folded nuclei and dense clustering
^cIn cases with grade 1 reticulin fibrosis⁸⁷, the megakaryocyte changes must be accompanied by increased BM cellularity, granulocytic proliferation, and often decreased erythropoiesis (that is, pre-PMF)
^dIn the absence of any of the three major clonal mutations, the search for the most frequent accompanying mutations (ASXL1, EZH2, TET2, IDH1/IDH2, SRSF2, SF3B1) are of help in determining the clonal nature of the disease
^eMinor (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
^fBM fibrosis secondary to infection, autoimmune disorder, or other chronic inflammatory conditions, hairy cell leukemia, or other lymphoid neoplasm, metastatic malignancy or toxic (chronic) myelopathies

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