Distribution of hematocrit level in JAK2 V617F-positive disease. (A) Diagrammatic representation of hemoglobin levels in patients with JAK2 V617F-negative ET, V617F-positive ET and V617F-positive PV, showing mean hemoglobin levels for patients with V617F-positive and negative ET (from Campbell et al⁷ ) and V617F-positive PV (from Cambridge cohort); hemoglobin levels in the mid-range will include patients with both ET and PV. (B) Hematocrit levels at diagnosis from a cohort of patients attending the Cambridge MPN clinic and diagnosed with JAK2 V617F-positive ET or PV, showing considerable overlap in hematocrit between ET and PV in both male and female patients.