It is now nearly two years since the publication of the 2016 revision to the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia [1] with one of the most controversial updates being the revised criteria for the myeloproliferative neoplasm (MPN) of polycythaemia vera (PV). The new major criteria for PV included a lowering of the diagnostic haemoglobin level (Hb; >16.5 g/dL in men and > 16.0 g/dL in women) and haematocrit (HCT; >49% in men and >48% in women) and the inclusion of bone marrow morphological features, in addition to the presence of a JAK2 V617F or exon 12 mutation.
