C4B and acquired polycythemia vera: At the time of recruitment, 648 individuals (of whom 233 had CH driver mutations) had been previously diagnosed with a myeloid neoplasm and an additional 108 had, according to the latest diagnostic criteria17, blood count results that were consistent with a probable diagnosis of polycythemia vera (n = 26; hemoglobin concentration (HGB) = 17.9 ± 1.43 g dl−1 and JAK2-V617F variant allele fraction (VAF) = 0.38 ± 0.2, mean ± s.d).