JAK2 and nutritional disorder: Serum iron (22 μg/dL [normal range, 60–160 μg/dL]) and ferritin (5 ng/mL [normal range, 15–200 ng/mL]) were suggestive of iron deficiency, serum erythropoietin was 8 mU/mL (normal range, 4.0–18.5 mU/mL), and a Janus kinase 2 (JAK2) mutation analysis was positive for JAK2V617F.