Approximately 1% of persons with homozygous sickle cell disease also demonstrates hereditary persistence of fetal hemoglobin (HPFH). Persons with Hb S/HPFH have a milder anemia than individuals with SCD who have none to normal levels of Hb F.
Increased fetal hemoglobin protects the cell from sickling because of its higher affinity for oxygen. HPFH may also be present in conjunction with other hemoglobinopathies (like sickle cell disease) and thalassemias, such as Hb SC/HPFH and Hb S/Bthal/HPFH.
