Among patients with ET, those with a CALR mutation had a lower hemoglobin level, a lower white blood cell (WBC) count, and a higher platelet count at diagnosis than patients with mutated JAK2. 7–10,22 Patients with JAK2V617F had a lower serum erythropoietin than those with CALR mutation. Here, JAK2 is linked to essential thrombocythemia.