“…Although it is certainly difficult to tackle the very beginning of PV, it is tempting to assume that in the series of patients previously described to present idiopathic (pure, benign) erythrocytosis or an occult/smouldering PV, a considerable number may be consistent with initial disease manifestations [63][64][65][66][67], but particularly those with positive JAK2V617F mutation status and high allele burden [3,10,15,28,29,[68][69][70]. As shown by an elaborate epidemiological study in 88 patients with an confirmed high hematocrit level (women >0.48, men >0.51) after an observation time of 5 years progression into manifest PV [5,7] occurred in three patients [71].…”