Hemoglobin F synthesis is not restricted to fetal erythropoietic organs during extramedullary hematopoiesis.

We investigated whether the anatomic distribution of hematopoietic cells determines the type of hemoglobin produced in patients with extramedullary hematopoiesis (EMH). Fetal hemoglobin (HbF) production is not restricted to fetal erythropoietic organs during EMH. A shift of erythropoiesis to fetal hematopoietic organs in EMH does not necessarily induce HbF synthesis in adulthood.