Frequency of polycythemia in individuals with normal complete blood cell counts according to the new 2016 WHO classification of myeloid neoplasms

Introduction: Polycythemia vera (PV) is a disorder characterized by clonal proliferation of myeloid cells and increased red blood cell mass. Recently, the revised 2016 WHO classification of myeloid neoplasms decreased the threshold levels of hemoglobin and hematocrit for the diagnosis of PV. However, the new proposed cutoffs have remarkable overlap with the normal reference values reported and the clinical impact of these new cutoffs has not been widely assessed in the general population. Methods: We retrospectively examined 248839 patients with presumptively normal complete blood cell results, consecutively obtained in an outpatient setting. Results: The proportion of men with Hb >165g/L was 5.99%, Hct>49% was 2.4%, and Hb >165g/dL or Hct>49% was 6.48%, while the proportion of women with Hb >160g/L was 0.22%, Hct>48% was 0.11%, and Hb >160g/L or Hct>48% was 0.28%. Conclusion:The isolated use of the proposed Hb/Hct levels as a definer of polycythemia may lead to a substantial increase in unnecessary diagnostic tests. In cases with borderline levels of hemoglobin, the diagnostic workup of PV should only be indicated in the presence of clinical and/or laboratorial features associated with MPN.