Model of relative erythropoiesis and megakaryopoiesis based on JAK2/MPL mutational status in essential thrombocythemia (ET). JAK2V617F positive ET is characterized by a relative increase in erythropoiesis, which manifests as a higher hemoglobin level and reduced erythropoietin level, whereas MPL-positive disease or MPL/ JAK2-negative disease is associated with higher platelet counts and reduced hematocrit.